Well really the only thing that will do that would be a bad throttle position sensor, or a major vacuum leak. A stuck open idle air control valve can cause this, but it would have to be wide open. What vacuum hoses were repaired? Was it done correctly and reinstalled correctly? How about the brake booster hose? It could be off, or the booster could be bad.
TPS is new. Major leak was located & fixed on vapor line to motor near the brake booster( line rubbed thru booster bolt) it idles fine when cold. but after appx. 50 miles check engine light came on w/ codes p0404 and p1404. Then started idling @3k again. EGR valve appears to be new also.
That is useful information. The two codes you are setting are for the EGR system. Obviously the EGR valve must be sticking open causing the vacuum leak and high idle. There could be carbon build up that is getting stuck in the pintle valve of the EGR and causing it to stay open when it shouldn’t.
Another tech replaced the valve last month. That doesn’t mean it is functioning properly. New parts go bad all the time, especially if it’s an aftermarket part.
It’s a GM part so I didn’t take it off & check it yet. could it be caused by an intake gasket after its warmed up?
Have never seen an intake gasket on the 3.4 cause that problem. When they are bad, they usually just leak coolant and oil, not cause a vacuum leak. I’d stay in the EGR area to locate the problem since you are setting codes and that’s when it acts up. You may want to remove it and check for debris, and also give the port a very good cleaning. The carbon that builds up in the that passage does also makes it’s way up the idle air control valve. If a piece gets stuck up there it can cause it to not function.
Previously it had many EVAP/emissions codes so I repaired what was wrong but the high idle continues.
The problem will continue if you have little pieces in the system. One after the other will get caught up in the EGR valve. EVAP problems will not cause a high idle.
According to the repair manual the evap/emissions is a common problem causing high idle. but as a Ford master tech I’ve seen many misprints. gimme a power stoke any day of the week and I’m happy.
I hear ya, but with almost 20 years of GM experience, I have never had an EVAP component cause a high idle problem like you are experiencing. I guess anything is possible, but the EGR codes do need to be addressed, and I’m sure will fix your problem.
Well thanks for the info. I’ll check the EGR/IAC systems and give this thing a good second look. Then do the brakes cause the owner kept driving it til the pads went metal to metal.
No problem at all. Have a great night!