Stuck at low RPM when driving - rough idle

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Stuck at low RPM when driving - rough idle

Postby ash10hunt » Thu Jun 17, 2021 6:48 pm

I just fixed my fuel injector and coil pack problem, and have been dash light free for the first time in awhile, but now my q45 will get stuck at around 1000-1200 rpms while driving, and then eventually take off. It also usually has a rough start up/idle at lights as well. This was happening while I had a code and TCS and SLIP lights, but when I fixed those I thought this would be solved too. I don't have any codes or indicators of whats wrong so I don't really know where to begin. The only thing I can think of is maybe throttle sensors? But I'm assuming something up with that would throw a code. Any ideas are welcome, I just need some kind of lead.
Thank you

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Re: Stuck at low RPM when driving - rough idle

Postby 3Q Jay » Sat Jun 19, 2021 10:30 am

Throttle position sensor unlikely, but I did have one intermittently fail on the FGY33. I never did a forensic sectioning, but observables were consistent with dirty wiper on the pot. Best way to confirm/rule out is to map the TPS voltage over throttle position. TPS voltage sweet spot is Exactly 0.44v at warm closed throttle.
Yours also sounds more like a MAF problem, but again, data is the key.

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Re: Stuck at low RPM when driving - rough idle

Postby Q451990 » Sat Jun 26, 2021 9:33 am

From your other thread, you were having injector issues that you've fixed. I think it's possible that your spark plugs are badly fouled. I had this with one of my injector failures. The plug on the corresponding cylinder was completely black with carbon and not firing.

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