Junior Member, warming up (<31 posts)
Join Date: Apr 2019
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Slightly rough idle on warm engine only?
Hi! Would like to ask for support & advices.
On my BMW E60 M5 since I have bought it (1,5 years, almost 30k km driven already) I have an issue with slightly rough idle, but only on a warm engine. The issue is more noticeable in case the engine idles a lot e.g. in a traffic jam. Possible to feel then some vibration as well.
Idle control valves have been replaced, but nothing has changed. Throttle bodies have been cleaned as well. Vacuum leaks have not found.
No trouble codes identified.
Some days ago have noticed that MAF sensors show different intake temperatures on bank 1 and 2 i.e. on a hot engine the difference is sometime 5-7 Celsius. Have tried to switch the MAF sensors between banks, but ISTA shows same date i.e. MAF sensors are probably fine. Could it be a MAF wiring issue or such difference might be simply because the air is really warmer in some parts under the hood?
Unfortunately, did not have a chance to check if MAF sensors should different temperatures on a completely cold engine.
I understand that in theory different intake temperatures on banks may cause some rough idle due to different fuel mixtures. Could it be true?
Mass air flow values on idle are shown by ISTA as quite identical on both banks. About 18-19 kg/s if I remember correctly.
Any advices where I could dig further? Do not really feel any effect on performance from this slight rough idle issue, but still would like to finally solve it.