03 5.4 - Idle Air Control Valve or...?

[Eric M]

The Exp has been running great since the head gasket replacement (getting 18-19 mpg on the highway).

Th only lingering issues are two codes, that are probably not related to the issue I'll describe below (both the C1284 and P0552 are for low voltage to the oil pressure sensor and PS pressure sensor, which are most likely caused by me having damaged the harness/plug, which got tugged on a lot during the rebuild. Next time I'll know to unplug everything beforehand.)

Anyway, the car starts fine and the idle appears stable on the data livestream. But, after coming to a stop it hesitates/stumbles when accelerating, which inmediately disappears after it gets rolling. I was watching the livestream as it stumbled and the RPMs did not drop. It shows no signs of hesitation or reduced acceleration at higher speeds. No misfires. BUT, my wife said it stallled on her twice when accelerating from a stop.

Having dealt with vacuum leaks on this car before, this doesn't feel vacuum related to me. All the ignition components are basically new (no more than 1k on them). The fuel pump was replaced about 80K ago and has never had problems. It threw a code for the MAF a couple of weeks ago, but that was corrected with cleaning.

Might his problem be caused by the IAC?

 

[Hamfisted]

Do you notice the idle dropping below 500 when you come to a stop ? If not, then the IAC is probably fine. Maybe dirty, but functioning. Do you see an erratic reading from the MAF in live stream when this stumble occurs ? You said you clean it and whatever code didn't come back. But there could still be an underlying issue with the MAF. That and the throttle position sensor there on the throttlebody control computer imputs during acceleration.











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[Eric M]

Thanks for the info. Idle is fine at stop. After posting I also began thinking about the MAF again and that it sometimes doesn't throw a code. I haven't had a chance to look at the MAF live stream, which I will do next.

 

[Eric M]

Given the MAF and the TPS appeared to be original (with 186K on the clock) and the new replacement parts are not very pricey, I decided to replace them both and problem solved. Thanks again for the help!