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Hello all, first time posting, so please forgive any mistakes I make. I drive a 2002 base model manual, completely stock, and my issue is as follows.
Sometimes when I'm driving, the revs jump by 1 or 200 rpm then fall slowly when upshifting, making shifting take longer than usual. This problem is common, but intermittent, and sometimes the revs will fall like a rock like they should every few drives. With the AC on, this problem is made worse. Shifting from 5th to 6th gear at 50 miles per hour is impossible because the revs won't drop enough to where I can smoothly shift into the gear. 1-2 shifts take 2 seconds or more, and the revs seem to want to stay at around 1500 when I'm shifting.
Additionally, sometimes when rolling in neutral the idle will stay anywhere from 1100 rpm to 900 rpm, then drop to 750 when completely stopped.
From what I've researched so far, the cause of this is most likely a vacuum leak, but I'd appreciate any insight beyond that or anything in particular I should watch for.
Could be a vacuum leak…has the battery been replaced or any other maintenance recently done and when was the last time the throttle body was cleaned or inspected ??…if you have a scan tool you can check for a vacuum leak by looking at your fuel trims.
sounds like a vacuum leak. Throttle body cleaning and ensure the sensor is firmly plugged in is first thing I'd do. It can't hurt to clean your TB anyway. It's likely due.
The battery was replaced approximately 2 months ago, but was disconnected just last week for some maintenance I was doing on it. How does the battery impact the rev hang?
I will jiggle the sensor (I assume the MAF?) and then inspect the throttle body. I am mechanically inclined, but new to this car, is the throttle body cleaning something I can do in my garage? I've replaced the starter and water pump by myself, and I wouldn't assume the throttle body is especially difficult to service.
I do not have a scan tool, but can borrow one from an auto store. What should I be looking for to confirm a vacuum leak? What's the easiest way to isolate where said leak is coming from?
Since the battery was disconnected you will need to perform an “idle learn” procedure…is your car an auto or M6 ??…you can try that…please fill out your profile so we know what we are dealing with !!…below is procedure for both.…it says idle will be unstable if those items were done to the car…good thing you mentioned the battery was disconnected last week or we would have been chasing our tails !!…let us know if it works.
To your other questions... the TB is very easy to access and clean. Just requires removing the airbridge from the TB. Then some brake parts cleaner or TB cleaner on a rag or paper towel to wipe the bore and blade clean. The sensor I was referring to is the TPS (throttle position sensor) located on the left (passenger) side of the TB. Ensuring the MAF sensor is plugged in accordingly is another one I'd check.
I just completed the relearn idle feature for my car, it made no difference in the behavior. It is slow to drop revs, will not idle at 750 unless stopped, and 'blips' the revs occasionally by 1 or 200 rpm when upshifting.
It is currently pouring rain outside, and my car does not have a garage home, so the TB and TPS inspection/cleaning will have to be delayed.
Also something to consider: sometimes it works like it should. On the 30 minute drive I just took, and the 15 or 20 times I put it in neutral at 40 MPH, two times the revs dropped like a rock and stayed at the 750 idle number while rolling. Every other time it fell slowly and hovered around 950 - 1000.
I will update when I am able to work on the TB and TPS, thank you for the help. Any other recommendations or general advice in the meantime would be greatly appreciated.
Does your cruise control work as expected? i.e. you can enable cruise control while driving along, and then pushing the clutch pedal in disables it ? Just looking to rule out upper clutch switch as a culprit.
Mine did the exact same thing for a few years. I finally figured out the injector orings were hard as a rock and sucking air. Found by using a propane torch OFF and spraying the manifold area while watching the O2 sensors on a graph go up and down.....as soon as I hit the injectors the O2s pegged high.
2002 C5 extreme rev hang
sounds like a vacuum leak. Throttle body cleaning and ensure the sensor is firmly plugged in is first thing I'd do. It can't hurt to clean your TB anyway. It's likely due.
