intermittent high/hanging idle

[corey5988]

I've had this problem intermittently for the last month or two. I only seems to do it after warm up. The car will basically act as if the throttle is stuck. I can feel the car pulling/holding speed if I take my foot off the throttle with it in gear. When I go to clutch it to change gears the RPM will jump up. When i pull it out of gear the RPM will steadily climb to around 3k and hang there for 5 seconds or so, then ease down. Like I said, it's intermittent and I see this happen maybe 1/4 of the time I drive it.

I did have CEL for P0113 - Intake Air Temperature Circuit High Input recently. I replaced the IAT sensor in my manifold and added a vented oil catch can to keep oil off the sensor (the sensor I took out had oil on it). That was around a week ago. I have yet to see that code again, though I still occasionally get a P0133 -Oxygen Sensor Circuit Slow Response (Bank1, Sensor1) CEL. I have long tubes, and from what I've found this is a very common issue with them. I have no other CELs.

Background on my car is it has a Roush factory installed M90 blower. I have the JBA long tubes, OR/H, GT500 TB, and remote tuned. I did just load a revised tune the other day. However this problem was present before then, and is still present.

 

[BruceH]

It's usually a tuning issue. Specifically dashpot and idle air. Too much air is being commanded at drive idle imo. Give your tuner a chance to work it out. If he's making revisions for you it means he's trying. Not every combination is easily custom tuned.

 

[corey5988]

It's usually a tuning issue. Specifically dashpot and idle air. Too much air is being commanded at drive idle imo. Give your tuner a chance to work it out. If he's making revisions for you it means he's trying. Not every combination is easily custom tuned.

The revision was in relation to other changes. My thinking was since it was so intermittent that it wasn't tune related. I didn't mean to come across as a hit on the tuner, as they have been a pleasure to work with. I didn't want to worry them with something that may waste their time. Since it may very well be in the tune I'll go ahead and get with them on it as well. Thanks.

 

[BruceH]

The revision was in relation to other changes. My thinking was since it was so intermittent that it wasn't tune related. I didn't mean to come across as a hit on the tuner, as they have been a pleasure to work with. I didn't want to worry them with something that may waste their time. Since it may very well be in the tune I'll go ahead and get with them on it as well. Thanks.

It could be other things like a vacuum leak. I didn't realize it had just popped up. Did it just come up when you went to breathers? How well did you seal off the pcv intakes when you put breathers on?

 

[corey5988]

It popped up a month or two ago. I went to the vented catch can around a week ago. That setup is sealed pretty good. I was thinking something along the lines or electrical/sensor since it only occurs 1/4 of the time and only after warmed up. Also on my boost gauge I haven't paid attention to vaccum at idle, but at full boost it's showing 6#.

 

[corey5988]

Boost gauge is reading 20# vacuum at idle and 6# full boost.

 

[Corpo]

Can you post some pics of your engine bay, show how you routed the hoses to your catch can please.

 

[corey5988]

Can you post some pics of your engine bay, show how you routed the hoses to your catch can please.

I can try to snap one in a bit. I just have a hose off both valve covers. They come together at a tee and then directly into the catch can, which is vented.

 

[blownGTvert]

Intermittent issues can be difficult to diagnose. If it was a vacuum leak or tune related it would be more prevelant and/or constant. You may try replacing the TB motor. It's only a $50 part and easily replaced.

 

[Corpo]

I can try to snap one in a bit. I just have a hose off both valve covers. They come together at a tee and then directly into the catch can, which is vented.

Good enough. Don't need the picture. It isn't a problem.

 

[corey5988]

Intermittent issues can be difficult to diagnose. If it was a vacuum leak or tune related it would be more prevelant and/or constant. You may try replacing the TB motor. It's only a $50 part and easily replaced.

I have the stock TB laying around. I didn't think TB parts were replaceable though?

 

[blownGTvert]

I have the stock TB laying around. I didn't think TB parts were replaceable though?

The TB motor isn't available from Ford. But it is available through auto parts stores. Rock Auto has the Dorman part for $52. It could be tune related but seems odd its so intermittent.

 

[corey5988]

I assume that the TB motor would be the same from GT to GT500? If so I'll switch them out and see what it does.

 

[blownGTvert]

I assume that the TB motor would be the same from GT to GT500? If so I'll switch them out and see what it does.

Yes both use the same TB motor assembly. I looked up TB motor part number Dorman # 911102. The small torx head screws probably have blue loctite from the factory. Use a heat gun on them so they don't snap off.

 

[corey5988]

I switched out the TB motor assembly and still no resolve.

 

[corey5988]

It's increased to doing this the majority of the time now. Like said I swapped out the entire TB motor assembly with the same result. Only thing I can think of at this point is a vacuum leak. I've glanced over it and seen nothing, and my boost gauge is reading 19-20# at idle and 5# at full boost.

 

[blownGTvert]

It's increased to doing this the majority of the time now. Like said I swapped out the entire TB motor assembly with the same result. Only thing I can think of at this point is a vacuum leak. I've glanced over it and seen nothing, and my boost gauge is reading 19-20# at idle and 5# at full boost.

What does you tuner say about the issue? It could be tune related as Bruce mentioned above.

 

[corey5988]

What does you tuner say about the issue? It could be tune related as Bruce mentioned above.

I emailed them and included a link to this thread. Awaiting a response.

 

[SeanD]

I have the same issue with mine. I have Kooks LT with FRPP 62mm TB and JLT Series 3 CAI. When I come to a stop, the throttle hangs around 18-1900 rpm for around 5 seconds or so and then drops to a proper idle. When this happens, if I blip the throttle while stopped it goes right down to proper idle. I have a Bama tune and haven't had a chance to ask them about it yet, but from what I found while searching around, it is typically a tune problem.

 

[corey5988]

I got a revised tune. Going to load it up and see what happens.