Eratic idle helppppppppppppp!!!!!!!!!!!!!!!!!!!!!!!!!

[freddiehebert]

So wonder what you guys would check first or change. 1998 explorer engine with 1993 distributor with computer and wiring from mustang medic. have explorer fuel rail with injectors bbk 70 mm throttle body. Car runs fine drives fine, track days are fine has been driven to LA and back , So Lake Tahoe no problems driving. Commute in it a couple times a week.

Here is the problem car has eratic idle, sometimes will be fine idles nice and then other times has a surge up and down about 1000rpms almost where it will die than surges back up. This never happens constantly could change from stop light to stop light.
This is not a new problem it has been an on going problem just finally getting tired of it
Any tips would be great. Thanks in advance

[alpine227]

So wonder what you guys would check first or change. 1998 explorer engine with 1993 distributor with computer and wiring from mustang medic. have explorer fuel rail with injectors bbk 70 mm throttle body. Car runs fine drives fine, track days are fine has been driven to LA and back , So Lake Tahoe no problems driving. Commute in it a couple times a week.

Here is the problem car has eratic idle, sometimes will be fine idles nice and then other times has a surge up and down about 1000rpms almost where it will die than surges back up. This never happens constantly could change from stop light to stop light.
This is not a new problem it has been an on going problem just finally getting tired of it
Any tips would be great. Thanks in advance

Try cleaning the idle control valve, and check for any vacume leaks.

V/R
John

[OVCobra]

John has it right, either have an erratic idle air valve or an erratic vacuum leak or both.
Dave

[freddiehebert]

thanks guys got couple extra air valve here at the shop gonna try that let cross fingers

[Hans944]

My roadster was having a similar issue. I pulled off the idle air valve and cleaned it up and put it back on. It had some black carbon inside the valve and I cleaned it all out. I drove it for a little bit and still had the same issue. I decided to replace the idle air valve yesterday. It seems OK now. It was to cold to drive the car very much. If that doesn't do it I'll start searching for any vacuum leaks.

[Hans944]

I actually did already look for some vacuum leaks and didn't find any. If replacing the valve doesn't do it I'll continue to look for vacuum leaks or another cause.

[CraigS]

Don't forget to check that fitting under the intake plenum that has 3-4 vac hoses attached.

[skullandbones]

I'm not sure if a surging idle that is not happening consistently is associated with a vacuum leak unless the vacuum leak is also fluctuating or transient. It could be the fuel rail pressure changing. I also spoke to a tuner who thinks my surging could be due to tuning issues but he is trying to sell me on dynoing and new tuning chip so I have to judge that considering the vested interest. Sometimes mine idles and sounds great with a noticeable lope (E cam). Then the surge comes back. If I was listening to your explanation at the beginning of the thread, I would have thought it was the problem I was having (identical). Also, the valve in question is new and clean. I took the top of the engine apart for cleaning and polishing the valve covers and manifold. I did not encounter any possible leaks. Hoses were tight and intact. I'm thinking of adding a circuit to the cutoff switch that will maintain the power to the PCM to see if the "learning" files in the PCM will stay active instead of being wiped out each time I turn off the power.

Thanks,

WEK.

[Hans944]

Don't forget to check that fitting under the intake plenum that has 3-4 vac hoses attached.

CraigS:

Are you talking about the fitting on the driver's side under the plenum? I only have one vacuum hose going to it; from the PCV Valve. There is another port there that is blocked off with a rubber nipple. I checked the other vacuum hoses going to the black fuel canister in the engine bay. They look older but seem to be OK...

Any other places to check for possible vacuum leaks?

What seems to happen with my car is it runs and idles well until it sits for a minute or two idling then starts to run a little rough... When idling it sounds likes a loping cam then drops down. My car has a 5.0 Ford Racing crate motor (340 horsepower - stock)... When I accelerate it runs great! When I let off the gas it seems to backfire a little bit...

Thanks!

Hans

[skullandbones]

I heard about another possibility for surging on the Mustang forum. If you don't have a clutch safety switch hooked up the open circuit can cause a PCM code 67 that will cause the idle to be erratic at times. The solution is to connect the two wires to the safety switch or connect the two wires together. It's been so long since I wired mine using a AAW harness, that I will have to go back to see if I did that step. I know I didn't connect the clutch safety switch. I didn't install one. Instead, I opted for a internal trans safety switch so the trans has to be in neutral before starting the engine. I like that strategy better. However, I may have left that dedicated circuit unconnected. I will have to fish through the dash wires to see. Hope that's your issue as it would be an easy fix.

Thanks,

WEK.

[Hans944]

I think I may have solved the problem... I have made some improvements anyway and it is much better...

I cleaned the throttle body and my MAF sensor...Did it separately with the appropriate cleaners....

Additionally, I noticed I had Autolite 103 spark plugs installed by the previous owner... I read where the Autolite 103's were two steps colder from stock.... I went back to the originals to be used with the GT-40 aluminum heads... Motorcraft AGSF - 32C....

The car seems to run better and idle much better... We shall see from here....

[CraigS]

The throttle body probably was the main problem. On one model Lexus I used to work on at the dealer, we got to where we automatically added a throttle body cleaning to anything we did regarding how the engine ran. Don't know exactly why but we had a bunch come back w/ the idle too low after repairs. Cleaning the throttle body fixed it but, at that point, we were doing it for free.

[Hans944]

The throttle body probably was the main problem. On one model Lexus I used to work on at the dealer, we got to where we automatically added a throttle body cleaning to anything we did regarding how the engine ran. Don't know exactly why but we had a bunch come back w/ the idle too low after repairs. Cleaning the throttle body fixed it but, at that point, we were doing it for free.

Craig.... I used the Seafoam aerosol can to clean the throttle body.... I used about 1/4 of a can of it to clean it....

The roadster is running good now.... smooth idle....

Thanks for the reply...