1986 Honda Accord Engine vibration @ idle

Tiny
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  • 1986 HONDA ACCORD

Engine Performance problem
1986 Honda Accord 4 cyl Two Wheel Drive Automatic 131000 miles

Too much engine vibration when idling; the car rattles as it was going to fall apart. Engaging transmission amplifies the rattling. But once the engine is above 1,000 rpm the vibration subsides and car runs fine, gears shift smoothly.

No misfire felt; checked unplugging each wire to see difference and you can note the difference when a spark wire is unplugged. Same for fuel injectors; when unplugging one of them idle becomes irregular.

The other driving symptom is that when cruising at about 2,000 rpm (about 45-50 mph) I can feel like a slight hesitation; engine does not seem to have too much power at that speed range. Engine has power at highway speeds up to 80mph (I did not press further)

Car passed emissions without problems

Things I checked/replaced

Distributor cap/rotor/wires/spark plugs: new; wires resistance about 1k ohms.

Ignition timing adjusted. Mechanical and vacuum advance work including the cold advance.

Thermostat replaced.

Oxygen sensor replaced. Temperature sensor seems to work as engine changes behavior (idles slightly aster) when unplugging it with engine hot

Timing belt replaced and set at right timing @ TDC "white mark" (someone had confused the TDC mark with the ignition timing mark and car died when idling. I did this when replacing all the seals (car was leaking oil badly). Now it does not leak any oil; also repaired oil leak inside distributor (new shaft seal)

New PCV valve works OK. EGR valve works OK (no leaks)

No vacuum leaks, steady vacuum at about 20 mmHg at idle.

All engine mounts replaced.

Fuel pressure ckecked about 39 psi at idle with pressure regulator vacuum hose disconnected; pinching return fuel hose sent pressure up at about 70 psi (so fuel pump is OK?)
New fuel and air filters

I thought about sending fuel injectors to cleaning and removing intake manifold to check for carbon deposits at the intake valves. What else may be wrong?

Thanks

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Friday, December 26th, 2008 AT 9:54 AM

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Tiny
BMRFIXIT
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It sounds to me as balance shaft off
but I do not recall if the 1986 if had one or not
rechecking the timing marks would be my 1st step

also loosen motor mount bolts run engine shift to drive and then to revese
hold position for few
put in park shut engine off
tighten mount bolts

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Saturday, December 27th, 2008 AT 8:48 AM
Tiny
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I checked the 1989 service manual I have. I use that manual to do the checks in the 1986 accord I have as it is the closest thing I have. The 1989 accord engine do not have balance shafts with engines being the same (A20Ax).

I checked timing a few weeks ago when checking valve clearance; timing marks were correct ("T" mark aligned and camshaft pulley marks align with top of cylinder head.

I loosen all engine mount bolts twice. The first time I adjusted them in sequence as per manual -no change- Second time I left them loose and drove the car for a couple days. The car shook the same as before with mounts loosened. Later I re-tightened them without any change.

I will check sensors because the other symptom is lack of punch at low rpm. Service manual lists some sensors as possible causes.
My question is how do I check the MAP sensor without a harness? I checked wiring coming to the sensor and it is OK but I cannot check voltage when plugged; manual describes wire color for a harness adaptor but not for the MAP sensor or wiring itself.
I have a vacuum pump; is there any way to check sensor output when changing vaccum?

Thanks!

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Saturday, December 27th, 2008 AT 2:14 PM
Tiny
BMRFIXIT
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Tap into the back of the wire plug
measure volts as u pumping the vacuum pump
I would check the vacuum source and if good
unplug the sensor wire and check if better replace the sensor
I do not think it is the map sensor honestly

my next step will be a cylinder balance test
disconnect one cylinder at a time noticing the vibration and power lose
good luck

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Saturday, December 27th, 2008 AT 7:43 PM
Tiny
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I checked the MAP sensor vacuum. It measures 20 inHg. @ Idle. Unplugging the vacuum line from the sensor immediately kills the engine. I left it connected with a 'T" connector and vacuum changes w/engine load; for double check I connected another vacuum gauge in other point of the intake and the readings were identical.
I did not check the electrics though. The other sensor I was thinking about is the atmospheric pressure sensor located in the cockpit. Also, the accord service manual I have lists throttle position sensor as something to check when idle is rough/lack of power. EGR is listed under "rough idle" but I checked the system and there are no leaks (the valve was pretty clean).

I did the power check. The engine vibrates worse when unplugging any of the plug wires without any noticeable difference about which plug it is unplugged. It runs rough and you can tell the difference.

A few days back I did the same with the fuel injectors unplugging one at the time; it was the same case -engine running worse and without difference regarding which injector was disconnected.

This problem (vibration at idle) grew worse over time; also is noticeable a lack of power at low and middle range.
When I got the car it had a vacuum leak (broken brake booster) which I solved. Then the idle speed was fast so I cleaned and readjusted the idle valve (the one behind the throttle body w/water hoses attached to it) and idle became more regular. Later I removed and cleaned the throttle body (idle bolt was stuck).
Car vibrated badly when engaging A/C; the A/C fast idle solenoid was dead. I replaced it and that subsided until the vibration on the engine itself became worse. You can feel the low freq rumble even when the transmission is in neutral or park. Engaging transmission makes it to be transmitted to the whole car.
Funny enough, once the car starts moving the vibration stops and car runs normally although with lack of power at low speeds. It has no reaction unless I floor the gas pedal in which case it will downshift two gears and blast forward. Power seems OK at speeds above 55 mph.
Gas consumption also seemed to increase lately. No oil consumption and it does not burn oil; I have barely added any oil since fixing all the oil leaks.

I am running out of ideas. I may continue driving it until whatever is getting bad makes the car not to run anymore, but knowing these Hondas it might take forever for it to happen.

Ah, no computer codes (no dashboard light and LED on ECU does not flash any code)

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Sunday, December 28th, 2008 AT 1:27 PM
Tiny
BMRFIXIT
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Did you try to advance the timing a bit
do it by ear just to check

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Sunday, December 28th, 2008 AT 6:48 PM
Tiny
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I checked advance w/the lamp; it is almost right at the red mark.

I drove the car as it was for a while as things got busy and I could not give any attention to the car at all. But fuel economy was poor and car was unresponsive at low range (about 2k rpm), so I decided to do something about it. I removed the fuel injectors and sent them to a cleaning service.
I just got them today; I installed them and drove the car a few miles.
Bad and good news. The bad news is that idle vibration is still there although it seems to be vibrate a little less; more driving would be needed to make a better judgment.
The good news is that it drives a lot better; hesitation and lack or responsiveness are gone. Now tapping the gas pedal gets an immediate response from the car, and a little extra pressure on the pedal would downshift the transmission without a problem; before I have to floor it if I needed extra acceleration.
The before-and-after figures they sent me showed an increase of flow of about 10% on each injector. They said spraying patterns for the injectors were off too. I cannot tell on either but I can tell that the car has improved.

I'll drive it more, fiddle a little with ignition advance and go back. Sorry for being gone for so long!

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Monday, February 16th, 2009 AT 11:13 PM
Tiny
BMRFIXIT
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Its great news and NOT bad at all !
Let me know what happens
happy driving

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Tuesday, February 17th, 2009 AT 6:29 AM
Tiny
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I've been driving the car for a couple days. Cleaned fuel injectors have made some difference especially in performance; the car feels alive now. I cannot tell about fuel consumption as I have not refueled yet but I would expect improvement out of better flowing injectors and correct spraying pattern. Overall, money well spent

But the vibration at idle is still there. I still have to fiddle with ignition timimg although it was dead at the right mark and I know the distributor works OK (I disassembled it to replace the low shaft seal and inspected all the internals)
I am suspecting that something else is going on; as I do not know about automatics I wonder whether the problem is transmission-related.
Overall, transmission seems to work OK; it shifts smoothly and no strange noises come from it. The only "odd" thing is that sometimes when driving at speed (40+ mph) It would engage 4th gear with no problem and then you may feel like something else "engages" and the engine rpm lowers a little (torque converter lock-up?); Alternatively, that "engagement" ceases and the engine gains a few hundred rpm (about 500 rpm). This is the only noticeable thing; I checked the downshift (is that right) cable and it starts moving when the gas cable starts moving.

When I replaced the rear crankshaft seal (it leaked badly) I drained the torque converter and the transmission and put new fluid (the old one looked quite dark) I used regular Mercon III fluid (owner's manual specification for the year/model was Mercon/Dexron). However, after reading on some forums that you should use only Honda ATF, I decided to use an additive that supposedly increases the grade of the transmission fluid up to a level suitable to that of Honda ATF.
Although the vibration at idle is still there, the transmission now shifts even more smoothly than before.

Finally, I read a Honda service manual and for excessive idle vibration it suggests as causes
adjust idle speed
defective torque converter
It further suggests to inspect the oil screen for particles of steel/aluminum and if there is no cause for contamination (if found) replace the torque converter.
Unfortunately, you have to disassemble the transmission in order to see such screen (no oil pan)
Is it possible that the torque converter would cause this? How it may be checked?

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Friday, February 20th, 2009 AT 8:53 PM
Tiny
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I test drove the car yesterday on the freeway to check for the converter lock-up; the "engaging an extra gear" that it used to do is gone.
I can feel that the converter lock-up engages when the car goes uphill and disengages when it goes downhill but it is slight (you need to look at the tachometer to see the change in engine rpm). I cannot tell whether it was the cleaned injectors or the "enhanced" transmission fluid that make it work better.

Anyway, the vibration remains and after reading the service manual for my model car I suspect that the torque converter is the problem. No matter how I adjust the idle speed the vibration is there; it only disappears when engine revs higher than 1,000 rpm

Assuming the torque converter is defective, should I go ahead and replace it at once? I wonder about the risk of it shoveling the transmission with shavings and debris if left for an extended time?

Thanks for the help!

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Saturday, February 21st, 2009 AT 12:53 PM
Tiny
BMRFIXIT
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Suspect tranny oil pump
you may have to remove and inspect
To verify if there's too much load on a fuel-injected car, check the voltage drop at idle between body ground and the EACV-to ECU wire. (For example, you'd check the BLK/BLU wire on a '90 Accord, or the BLU/RED wire on a '90 Prelude.) About 10V is normal. A reading of 2-4V indicates that the ECU and EACV are compensating for some extra load. On a carbureted car, run a trans stall test. The stall RPM will be below spec if there's too much load.
If the above check confirms your suspicions, disassemble the trans and inspect the oil pump for signs of seizure. If the pump is OK, the lock-up shift valve may be binding, which causes the lock-up clutch to partially engage. If the lock-up shift valve works properly, the only possible cause left is a casting flaw in the main valve body.

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Saturday, February 21st, 2009 AT 5:23 PM
Tiny
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Hi,

Just to clarify a little on the lock-up operations.

The lock-up should disengage when going up hill and engage when going down hill. Your description seems to say the opposite.

Improper trans throttle cable adjustment would cause the following:
1. Too short = Excessive pressure. Would cause harsh shifting and early downshift and late upshift. Surging while cruising would happen when lock-up engages and disengages with the slightest throttle movement or road condition.

2. Too long = Low pressure. Early upshifting and lack of accelerating power when flooring the pedal.

Try using a jack to support the engine slightly and see if the vibration goes away. It could be the engine mounts that are bad. For this model it goes bad rather quickly.

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Saturday, February 21st, 2009 AT 8:45 PM
Tiny
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Hey,

Thanks for the reply. I am unfamiliar with the nuts and bolts of automatics; I've been around sticks since age 10 so I know about manual transmissions and how to know whether they work fine or have a problem. As for automatics well. I may need to learn now.
On second thinking my description was incorrect; if the torque converter multiplies torque it should allow the engine to rev faster when driving uphill (more power is needed), and conversely when going downhill. Still, I notice the shift being quite imperceptible now.

Thanks for the trans throttle note too. I re-read the Honda service manual and it says that it is permissible to adjust it to "shorten it" if desired (but by not more than 3 mm.) Now it will start moving the lever in the transmission as long as the throttle is moving.
So if I shorten it a little I would have a more immediate response to downshift when pressing the gas.

I replaced all the engine mounts a few months ago; vibration has not changed. Tried adjusting them twice (as per service manual) but it did not help

BMRFIXIT: The car is EFI but it does not have an EACV valve -the 89 accord has such a valve but not the 86. Instead, the 1986 has a idle valve that sits close to the brake booster with two hoses one coming from the air filter and the other going to the intake manifold. It opens when it is energized; if it is unplugged it closes and no extra air comes in.

As much as I dislike disassembling the transmission (it has no oil pan) your suggestion of inspecting the oil pump complements the service manual. If the oil pump is seizing or its screen is clogged with debris the symptoms would be the same, right?
Besides, sometimes I see operation of the idle valve when apparently there is no load on the engine. So there is some load coming from somewhere; what would happen if I do a stall test?

Thanks!

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Sunday, February 22nd, 2009 AT 9:10 AM
Tiny
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One last thing: I did a stall speed test today. After warming up engine and transmission I followed service manual recommendations to do it.
I tested in D4, D3, 2, and R positions waiting a few minutes between tests to cool the transmission.
Engine stall speed (as measured by dashboard RPM): about 2,750 rpm in all gears.
The manual specified a stall speed of 2,650 rpm for FI engines with acceptable boundaries between 2,500 and 2,800 rpm. Also says that stall speed should be the same in all gears.
Does this help in anything? Thanks!

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Sunday, February 22nd, 2009 AT 9:44 PM
Tiny
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The stall speed indicates no problem with all the clutches tested. If the strainer is clogged the trans would tend to slip at high speed when insufficient fluid can pass through.

Did you check the torque rod adjustment? It is the one from a bracket attached between the trans/engine and firewall?

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Monday, February 23rd, 2009 AT 6:27 AM
Tiny
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Hello to all,

Sorry for disappearing for so long!

School has driven me crazy the last few months. Besides, the car drives OK except for the nasty vibration at idle. We put the transmission in N when stopping at lights and the vibration is lower although I can still feel it.

Regarding the torque rod I replaced its bushings a while ago.

As said earlier, vibration is worse when the car is not in neutral or park. R, D4, D3, or 2 does not make a difference -vibration is higher when in drive. It seems to me that while the engine is in neutral the vibration is somehow isolated in the engine (although it is still felt).

I eventually go back into trying to solve the vibration problem but I want to learn more about auto trans and especially torque converters, since the service manual pointed out to them as one possible cause for idle vibration.
I saw an online video in which they showed a locked-up torque converter; it had a clutch-like device attached behind one of the turbines (I think the one that drives the transmission). I wonder how a torque converter gets worn out when the car is driven mostly around town with all the idling in gear. It seems to me that all that wasted "torque" idling should produce heat which in turn should accelerate wear. In other words, what parts get worn out in a torque converter?

Thanks a lot!

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Saturday, May 16th, 2009 AT 2:43 PM
Tiny
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Great to hear from you again.

Torque converters are maintenence free components that are supposed to outlast the trans and vehicle. For models of the era mentioned, I have yet to encounter any faulty ones. If it is a turque converter problem, you would have issues such as bogging down, loss or performance and maybe a little harsh shifting.

With the trans in N there is vibration indicatiing it should not be a torque converter fault.

Did you inspect the engine mounts condition and alignment?
Was the torque rod correctly adjusted?

I would still say it is the engine mounts condition and their alignments that is causing the problem.

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Saturday, May 16th, 2009 AT 11:26 PM
Tiny
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I replaced all the engine mounts, plus the ones in the top torque arm.
The one on the timing belt side was destroyed. They are OEM replacements (BeckArnley and Anchor if I remember right).

Anyway, the vibration did not change. OK at idle but bad when in gear (Ds or R). Once rpms climb above 1,000 the vibration disappears and car drives OK. Transmission works OK

I tried loosening and then tightening the mounts; nothing changed.

I've re-read the thread. One earlier posting talked about checking valve bodies for the lock-up valve that might partially engage. I' kind of lost; car is drivable so I do not pay a lot of attention to it but I'd like for it to work as it should again.

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Saturday, July 18th, 2009 AT 9:32 AM
Tiny
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Under the engine between the trans and engine, there is a rubber damper sitting on the crossmember. Check if the crossmember is bent and resulting in the engine assy sitting onto it. There should be sufficient clearance between the engine and crossmenber.

Loosen the upper torque rod and test if the vibration is lessened.

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Saturday, July 18th, 2009 AT 8:15 PM
Tiny
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I looked underneath the car; the crossmember does not look like bent or the engine sitting on it.

Need to loosen upper torque rod to see what happens. I'll post updates. Thanks!

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Saturday, August 1st, 2009 AT 3:45 PM

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