Eratic Idle

[Carlos]

I have a 94 Limited Edition with 173xxx miles on it. My problem is my idle is too low (3 or 400rpm) and sometimes to high (1200 rpm). Sitting in my driveway it will jump from a low idle to about 1200 rpm and then back down. Funny thing is it's intermittent. It will idle for a few minutes then jump to a higher rpm. I've taken it to 4 different mechanics and they all had different ideas, one is still scratching his head. The last one said I have a stuck valve and basically need an engine swap. How would a stuck valve cause a constant low idle then jump up? I changed the IACV, the throttle sensor, the coolant temp sensor, new plugs, wires, fuel filter, air filter and cleaned the MAF sensor. I'm at a loss. Anyone had a similar problem?

 

[Howard]

Sounds like the intake manifold is leaking. It may just need re-torquing down or you may just have a vacuum leak. That where I would start.

 

[hermitrl]

Does it have air conditioning? When the compressor kicks in, there is a switch that bumps the revs up to allow for the extra drag on the engine. Just a thought.

 

[Bottomlesspit]

Thinking about my similar experiences with these vehicles, along with advice from the Haynes manual...these are some likely culprits.
I have to agree that vac leaks are highly suspect with all those old rotting hoses under the hood.
1) VAC leaks- manifold, hoses, gaskets
2) Leaking EGR valve
3) Bad PCV valve...or leaking hose to it
4) Air filter old
5) Weak fuel pump
6) Bad head gaskets....do cylinder compression check
7) Worn timing chain
8) cams, valves
A lot of these things you can check yourself. Use a stethescope and check around for leaks. Soapy water, starter fluid, etc sprayed in spots can detect vac leaks. Inspect all rubber hoses...especially the undersides.
Good luck in your hunt...been there, done that too. Let us know..........
Ken

 

[provincelander]

My old 90 Toyota 4 runner was idling from approx 2500 down to 500. What it was , was a sticking EGR valve. Im not sure if your truck has one, if it does, start there. It was real fun driving home that day when it acted up!

 

[engera]

I recently ran into a very similar problem with my '94 X and here is what I did to fix it.

One day while driving down the road my X started sputtering and lurching as I would go down the road. When I got to a stop light the idle was all over the place, ranging from 300 to 1200 RPM so it either almost was stalling or trying to run me through the intersection. The check engine light came on and then turned off. I knew the ECM had thrown some codes so I stopped by AutoZone to get the codes read for free. The codes indicated a failure in the Throttle Possition Sensor and the EGR valve. The AutoZone guy recommended both along with the IAC (Idle Air Control) valve. I went home and replaced all three but the problem didn't go away. After about a month of jagging around with this (Including a day last at the Ford dealer) I finnally found that if I removed the connector from the IAC the surging stopped. The idle would not kick up when a load was applied like AC being on but at least it stopped surging. I did have to turn the idle up a bit because it was too low without the IAC's help. I eventually bit the bullet and ordered another IAC from the Ford dealer and the problem was fixed. Sadly enough I nailed this problem on the first day but the crappy IAC from AutoZone completely hosed me. Not knocking AutoZone but I will be more selective on the type of parts I buy from there.

Try disconnecting the IAC to see if the erratic idle goes away. Sorry for the long winded reply but I hope this helps.

 

[silver stripe]

i had the same issue with 1992 explorer
i started on a rapping parts change, like the
tps, and the other 2 sencesrs on the head, cant
remember the name of them right now, same thing, as when you unhooked them it acted like the problem was fixed, but was not. had the codes scanned, all fine, had my machanic play with it and he found that the problem was in the throttle body where the throttle cable goes, there is a spring ect.... thing there, and it was kinda sloppy, so i got a used one from the local auto wreckers, cleaned it and it fixed the problem.

just a thought for you, check it the spring ect.... is kinda sloppy, easier if you removed the throttle cable

 

[spta97]

Originally posted by engera
I recently ran into a very similar problem with my '94 X and here is what I did to fix it.

One day while driving down the road my X started sputtering and lurching as I would go down the road. When I got to a stop light the idle was all over the place, ranging from 300 to 1200 RPM so it either almost was stalling or trying to run me through the intersection. The check engine light came on and then turned off. I knew the ECM had thrown some codes so I stopped by AutoZone to get the codes read for free. The codes indicated a failure in the Throttle Possition Sensor and the EGR valve. The AutoZone guy recommended both along with the IAC (Idle Air Control) valve. I went home and replaced all three but the problem didn't go away. After about a month of jagging around with this (Including a day last at the Ford dealer) I finnally found that if I removed the connector from the IAC the surging stopped. The idle would not kick up when a load was applied like AC being on but at least it stopped surging. I did have to turn the idle up a bit because it was too low without the IAC's help. I eventually bit the bullet and ordered another IAC from the Ford dealer and the problem was fixed. Sadly enough I nailed this problem on the first day but the crappy IAC from AutoZone completely hosed me. Not knocking AutoZone but I will be more selective on the type of parts I buy from there.

Try disconnecting the IAC to see if the erratic idle goes away. Sorry for the long winded reply but I hope this helps.

Was the IAC on the '94 or the '00? I'm just got my new one (Motorcraft) for my 00 V8 that I'm hoping will solve my issues (well, with the truck anyway )

 

[engera]

The IAC

Was the IAC on the '94 or the '00?

The IAC and the rest of the write-up was on my '94. I believe IAC problems have been recorded on all years and engine types of Explorers on this forum. I hope it fixes your problem.

 

[spta97]

Cleaning made it worse (idle would go now higher than 500 RPMs) but the replacement fixed the problem! Amazing how such a little, inexpensive part can cause so much trouble.

I got mine from rockauto.com - It's around $60. Install was 2 minutes.

 

[Carlos]

Thanks for all the help in figureing out what my problem was. As it turns out I was getting ready to check my fuel press regulator and found the vacuum line almost off!! Pushed it back on the engine burrped and has been running fine since. I went thru 4 mechanics and a dealership (which by the way told me I need a new engine cause I sucked a valve) and none of them could figure it out. Not to mention they told me they did a vacuum leak check!! Anyway, thanks again for the suggestions and the help. This is truly a great forum.

 

[Hank3rd]

Where is the fuel pressure regluator. I am having a simular problem and have replaced numerous parts. I may want to look at that.

Thank you.

 

[Carlos]

The fuel Press. Reulator is located on my 94X on the foward left hand side of the throttle body next to the fuel rail. (looking aft) It made it easier to get to it by removing that 2 screw cover plate covering the throttle body. The regulator has a braided fule line coming out the top and the vacuum line is on the bottom. Good luck, if this didn't help let me know and I'll see if I can be more specific. :redexp: