01 QX4 idle up & down after warm up

[slidersgarage]

01 QX4 idle goes up to 1200 and back down to 750 after car runs and warms up. 3 different Techs have replaced everything under the hood you can buy,maf, o2 sensors, intake gaskets, injectors,cam sensors crank sensors, tps, and pvc valve. It had po300 miss fire codes but now there gone. Some where along this money spending this is it repair job, somone turned the idle stop screw on the throtle body, and they say I need a new TB. can this be recalibered? what should I do? Is this making the idle surge? Also if I snap the gas pedel it pops in the intake

[NJ 666]

Check the IAC valve resistance. I've seen the IAC chambers go pourus and coolant contaminates the valve,it shorts and pops the ECM more common on I30s though. No code P505? Try to get the throttle screw back to where it was. might have to reset the TPS as well.

When this occurs you can watch the timing start to "scatter" a little to try and stabilize the idle this may be the pop you're getting. Whats the alpha and self learn at? Never seen this before with the pop noise though.

Please let us know what you find. I've never seen this exact scenario. Good Luck.

[SteveTheTech]

I've got to agree with NJ. If your popping through the intake your timing is off.....allot.

Have any of the mechanics you had attack your car removed the idle control valve under the throttle plate? If you take the two screws out and remove the valve and there are any signs of antifreeze you have found the cause of you problem and you will need and ECM and a IAC valve.

How many miles are on it? What's the service history like? Is there any noise from the front of the engine while it is at idle?

[NJ 666]

Did anyone put a vacuum gauge on it? Vacuum leak could cause the surge and lean mis-fire on tip in. I was assuming a competent shop would have tried that.Any breaks between the MAF and the intake? Did they put a Nissan MAF in it? Seen plenty of aftermarket ones non fix a maf issue.

[slidersgarage]

Everybody was very helpful! vacume leak was the problem at 1 &3 injector.along the way someone went to napa and replaced the o-rings and the plastic cap at the end of the injectors. these caps made the groove for the o-ring to small and the o-rings flipped over in the injector bores causing a leak. A smoke machine was used, and you could see the o-rings leak with all new seals. the caps were removed and reinstalled and the car runs great. A call to Nissan was made and they don't make or list new plastic caps for the injectors,so what ever Napa is selling is wrong! Thanks again,I'll be back Jon E Johnson