Mechanics

ENGINE VIBRATION @ IDLE

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
Avatar
Ecogabriel
December 26, 2008.



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

BMRFIXIT
Dec 27, 2008.
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!

Tiny
Ecogabriel
Dec 27, 2008.
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

BMRFIXIT
Dec 27, 2008.
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)

Tiny
Ecogabriel
Dec 28, 2008.
Did you try to advance the timing a bit
do it by ear just to check

BMRFIXIT
Dec 28, 2008.
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!

Tiny
Ecogabriel
Feb 16, 2009.
Its great news and NOT bad at all !
Let me know what happens
happy driving

BMRFIXIT
Feb 17, 2009.
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?

Tiny
Ecogabriel
Feb 20, 2009.
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!

Tiny
Ecogabriel
Feb 21, 2009.
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.

BMRFIXIT
Feb 21, 2009.
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