Fast Idle issues

Tiny
BOBDFORD
  • MEMBER
  • 1989 FORD F-150
  • 5.0L
  • V8
  • 2WD
  • MANUAL
  • 130,000 MILES
This has been an ongoing problems for years.

At Idle, the engine will sometimes Idle at the normal 500-800 rpm but the engine light comes on and stays on, (no code flashing). However! When the engine feels like it, the engine will sometimes start Idling high at 2,000 rpm at which point the engine light goes out and does not flash any codes.

Years ago, I took it to the ford shop and they said they replaced the intake gasket and that "seemingly" fixed the problem for about four to five months. Then it went back to the same issues as noted above.

I think it is very odd that no codes are thrown and the engine light acts as noted above. And being a rather good shop mechanic, I have done everything I know, and replaced quite a few of the sensors, map, idle, oxygen, exhaust, etc.
Nothing improves it.

The one thing I have noticed is that many of the 1985 to 1993 Fords (302) right passenger side exhaust manifold has a factory (defect) crack that appears between the two middle exhaust ports and ford never recalled this defect. Thus I ponder if the exhaust oxygen sensor is causing the issues due to the leak in the exhaust manifold.

I know everyone yells vacuum leak (somewhere) but its hard to believe that with all the maintenance I have done (and a four month old new intake manifold replacement) that the vacuum leak is the issue. If that were the case, then it seems that there would be a continuous high Idle, not an intermittent high idle one week, low Idle the next week.

Any other thoughts or suggestions?
Do you
have the same problem?
Yes
No
Monday, June 3rd, 2019 AT 11:03 AM

31 Replies

Tiny
SCGRANTURISMO
  • EXPERT
Hello,

This sounds to me like you could have a vacuum leak. I would check the air intake duct, Vacuum lines, PCV and PCV lines, throttle body, intake manifold, and EVAP lines for any vacuum leaks. You would be surprised what a little air leaking can do to an engine. I have included a link below for you to go to.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

and

https://www.2carpros.com/articles/engine-idles-too-high

Please go through this guide and get back to us with what you are able to find out.

Thanks,
Alex
2CarPros
Was this
answer
helpful?
Yes
No
Tuesday, June 4th, 2019 AT 8:52 AM
Tiny
BOBDFORD
  • MEMBER
Thanks for the input and insights.

Even though it has its common colds and normal hiccups, I Love this 30 year old "Ford" truck as it hast failed me yet. Stuck in the 1970's and 1980's I guess.

As I stated previously, this has been ongoing for years (at least two decades) and In such I have went through this engine and done the carb-cleaner test in the accessible areas, meaning its hard to do the test in certain areas or around the back of the engine near the fire wall. Or without spraying other components.

Best of my failing knowledge and feeble mind, carb-cleaner and rubber hoses (maybe the nylon/plastic ones as well). Some don't like carb-cleaner as it can/will melt and brittle certain types hoses; possibly causing more problems and vac leaks. Thus as I stated, I have avoided those "blind" hard to reach and other areas where the spray and/or over spray cant be controlled. In such, WD-40 was my alternative in addition to carb-cleaner in certain areas as it too will indicate a leak.

In saying that, the one thing I have never done is check the brake booster for vacuum leaks as that eluded me, but that is a good call. So that might be the culprit or a contributor at any level, and definitely something that should be looked at just from the maintenance end as its a vital component.

Being that its an older model, maybe I will replace some of the vac-lines just for the hell of it as I agree they look a bit old, rough and dirty (but intact). But who am I to claim I can see vacuum leaks. It just seems that vac-leaks would be consistent, not intermittent when it comes to the idle issue.

Since this is a project restore and not a desperation of an everyday commuter, I will climb back under the hood and play around some more when time allows.

But as for the other I posted, Ford seems to have avoided the "right side exhaust manifold casting crack" that appears after certain model/year trucks of this era as I have been under the hood of many, some just to prove my claim, and every one of them had the casting crack in the same area!
In such, there is an Exhaust Oxygen Sensor down below where the two sides of the exhaust union.
Though this would be a constant pressure side (exhaust) and very little O2 ever coming or leaking in to the exhaust and reaching the sensor, I cannot help but to factor that in to some "slightly off" reading sensor reading. Outside of that, any backfire or escaping heat from the hot gasses, seems to be of concern as it might cause a flash fire or undue increase in heat to that side of the engine, thus causing problems to electric and other over a long period of time. But that is just my ramblings of insights.

It is also my belief that this crack occurs due to casting and stress from the weight of the exhaust pipe and components, but due to the age of the trucks effected, that issue is mote and speculation now. Lets just agree that Its not something a 6 pack and JB Weld or Pipe Wrap will fix. LOL
Maybe a header swap would fix the old beater issue when and if you have the money for the fix.

Lastly, and for others with plastic line leaks per the link you posted; some of these lines seem to be glued or formed together to the rubber connector. In such you cant remove the connections to easily replace. While you can cut and splice the hose my alternative is the "Liquid (rubberized) Electrical Rubber" (Star Brite Liquid Electrical Tape) and/or as well as electrical shrink tubing that can be used to cover/seal any small crack as to seal it up or after splicing as to ensure a better long term seal.
Still I recommend an entire replacement of the hose as this (and splicing) is only a short term fix and is not very pretty.

Thanks again for the Insights.

I will double check the brake booster.
Was this
answer
helpful?
Yes
No
Tuesday, June 4th, 2019 AT 10:45 AM
Tiny
KEN
  • ADMIN
I have seen the engine coolant sensor cause this problem. here is a guide to help walk you through the repair with diagrams below to show you how on your car:

https://www.2carpros.com/articles/coolant-temperature-sensor-cts-replacement

Check out the diagrams (below). Please let us know what happens.

Was this
answer
helpful?
Yes
No
Saturday, June 8th, 2019 AT 2:04 PM
Tiny
BLACKOUTFORD
  • MEMBER
  • 1989 FORD F-150
Electrical problem
1989 Ford F150 V8 Four Wheel Drive Automatic

my check engine light comes on after about 10-15min. Of driving but goes out after I shut the truck off(whether while driving or stopped). I think it may have something to do with the emmissions stuff because I have already tried giving it a full tune up including plugs, wires, cap, rotor, oil change, and filter changes to at least eliminate the possibility of being an ignition or fuel problem. If it aids any in your answer, when I start my truck up, my truck has a high idle-around 1000RPM's and seems to rev itself as if the computer thinks it may stall or can't find the TP. This high idle and revving problem has been there for more than 4 years but had no check engine light.
Was this
answer
helpful?
Yes
No
Saturday, December 26th, 2020 AT 1:13 PM (Merged)
Tiny
JACK42
  • EXPERT
The idle problem sounds like a vacuum leak. Have the ECM scanned for codes to see what it has stored, this will help figure out what the check engine light is coming on for
Was this
answer
helpful?
Yes
No
Saturday, December 26th, 2020 AT 1:13 PM (Merged)
Tiny
DN_MARTZ
  • MEMBER
  • 1989 FORD F-150
  • V8
  • 2WD
  • AUTOMATIC
  • 118,000 MILES
Hello there, ---, engine starts great---goes into high idle for a few seconds then when it comes down to the normal idle it just dies like you shut the key off.--- Restart---goes into high idle again ---comes down and dies on the 3rd restart it always keeps running after it comes off high idle. Runs great after this---speed is no problem. It acts as tho something needs to sence heat before proper operation---
thank you----don
Was this
answer
helpful?
Yes
No
Saturday, December 26th, 2020 AT 1:13 PM (Merged)
Tiny
DOCFIXIT
  • EXPERT
Hi
Maybe a faulty temp sensor on right front side intake. Also remove idle air by-pass solenoid and clean pential and passage way. Is check engine light on?
How many miles on plugs?
Let me know
Thanks for donate
Was this
answer
helpful?
Yes
No
Saturday, December 26th, 2020 AT 1:13 PM (Merged)
Tiny
DN_MARTZ
  • MEMBER
Hi--cleaned idle by pass solenoid----(CRC ELECTRIC CLEANER) checked MAF sensor at auto zone--OK.---Will check temp. Sender --- found out that if I give just a little more RPM s to eng. While in high idle it will keep running so long as you hold it there at least 20 seconds before letting off.--- Still makes me think heat sensor.---Don PS-- this truck was in storage over 2 years when I bought it--wouldnt start till I installed new plugs---battery was dead when it was bought. Has not been driven more than 5 miles since bought---do you think that the computer needs a 15 or 20 mile drive to re-calibrate.---Runs great at hi RPM.----Don
Was this
answer
helpful?
Yes
No
Saturday, December 26th, 2020 AT 1:13 PM (Merged)
Tiny
DOCFIXIT
  • EXPERT
Ohm check temp sensor across terminals on sensor at 100 deg read 16150ohms at 194 deg read 2800 ohms. Disconnect battery for few minutes hook up and drive this should ECM to reset.
Was this
answer
helpful?
Yes
No
Saturday, December 26th, 2020 AT 1:13 PM (Merged)
Tiny
TDEFFENDALL
  • MEMBER
  • 1988 FORD F-150
I have a 1988 Ford F150 4.9L - 5 Speed Manual, 77K Miles. For what ever reason, after the truck has been running for a while (warmed up) when I engage the clutch to shift the engine revs. Up into Hight Idle (a little over 2K), this does not happen all the time, notice it happening when I am in areas that require a lot of shifting. When it jumps into High Idle, if I shut the truck off, start it back up, it is fine, any ideas?
Thank you
Was this
answer
helpful?
Yes
No
Saturday, December 26th, 2020 AT 1:13 PM (Merged)
Tiny
JESSE777
  • MEMBER
Possibly the TPS, throttle position sensor. Accurate testing requires $ophi$ticated shop equipment. Perhaps you have a pick and pull salvage yard where you can acquire one cheaply for test purposes.
Was this
answer
helpful?
Yes
No
+1
Saturday, December 26th, 2020 AT 1:13 PM (Merged)
Tiny
CHAD BLAHNIK
  • MEMBER
I had a 92 f-250 doing the same thing and by replacing the tps it ran fine
Was this
answer
helpful?
Yes
No
Saturday, December 26th, 2020 AT 1:13 PM (Merged)
Tiny
INDYUKE
  • MEMBER
I have an 88 f-150 as well, and I was having the same problem. Only it would happen constantly. It was the throttle position sensor.
Was this
answer
helpful?
Yes
No
Saturday, December 26th, 2020 AT 1:13 PM (Merged)
Tiny
TDEFFENDALL
  • MEMBER
Thank you everyone, I will try the sensor, it is only a twenty dollar part so it will be a cheap try.
Thanks again, I will let you know if this worked.
Was this
answer
helpful?
Yes
No
Saturday, December 26th, 2020 AT 1:13 PM (Merged)
Tiny
JESSE777
  • MEMBER
That is a great price. Normally I don't recommend replacing a part without diagnosis, but proper diagnosis is not cheap for this one.
Was this
answer
helpful?
Yes
No
Saturday, December 26th, 2020 AT 1:13 PM (Merged)
Tiny
RACER37L
  • MEMBER
  • 1987 FORD F-150
Engine Performance problem
1987 Ford F150 V8 Four Wheel Drive Manual

what would cause the engine to idle up after engine is warm and truck comes to a stop with the clutch pushed in?
Was this
answer
helpful?
Yes
No
Saturday, December 26th, 2020 AT 1:13 PM (Merged)
Tiny
BLACKOP555
  • EXPERT
The IAC valve may need cleaning the pintle might be sticking. Or the throttle cable slightly sticking.

Disconnect IAC connector and see if problem fixeds.

Could be a vaccum leak.
Was this
answer
helpful?
Yes
No
Saturday, December 26th, 2020 AT 1:13 PM (Merged)
Tiny
DICKIE
  • MEMBER
  • 1987 FORD F-150
  • 6 CYL
  • 2WD
  • MANUAL
  • 164,000 MILES
On July 26 I asked "1987 Ford f-150, straight six. Starts but I have to keep reving the engine until it warms up. Once it warms up it will idle at 550 to 700 rpm for a few seconds, and then slowly (3 to 4 seconds) idle up to 2500 to 3000. When I turn it off and restart, it idles at 1500, quickly goes to 550 to 700, then slowly climbs to 2500 to 3000. Over and over. When I disconnect the iac it wont idle at all, but will run if I pedal the gas. Actually changed the iac, but no different. Not sure what to check next. Old dirty engine."

hmac300 replied "clean the throttle plate with choke cleaner and check for vacuum leaks with the choke cleaner around intake ports andthrotle plate connections. Then taek out your egr vvalve and see ifit's all gunked up around the pintle valve inside. It may bestuck open ornotworking right."

pretty sucky answer. I guess thats all I get for $20. Anyway, I did a little more tinkering. Changed a bunch of vacuum hoses. No different. Changed pvc valve. No difference. Unplugged green hose from egr. No difference. Upplugged the electronics from the egr. No difference. Pinched off difference hoses (brake booster, cruise control, heater control) to see if engine would change noises. Nothing. The idle pattern is extremely repeatable. Once warmed up, on restart without pressing gas pedal, engine starts at 1500, settles at 550 to 650 for 2 or 3 seconds, then climbs to about 2500 in about 4 seconds and stays there. Over and over and over. Something is getting a rotten signal from somewhere. I even unplugged the battery to see if it would reset. Could it be the pcm? If I take the pcm out can it be checked?
Was this
answer
helpful?
Yes
No
Saturday, December 26th, 2020 AT 1:13 PM (Merged)
Tiny
FIXITMR
  • MEMBER
Any luck yet. Have you watched throttle linkage at body when this happens to see if it moves at all?
Was this
answer
helpful?
Yes
No
Saturday, December 26th, 2020 AT 1:13 PM (Merged)
Tiny
FIXITMR
  • MEMBER
And what about monitoring voltage to IAC?
Was this
answer
helpful?
Yes
No
Saturday, December 26th, 2020 AT 1:13 PM (Merged)

Please login or register to post a reply.

Sponsored links