I don't know if this is a "Yo-yo" problem or something else. When I shift at relative low rpms (<5000 rpm) driving easy and let off the gas as I shift the rpms don't just hang, they actually increase a little (200 or so rpm). This makes smooth shifting very hard. I actually have to lift before stepping on the clutch, and sort of coast a little, in order to match rpms. This is a pain in the ***. I have a lightweight flywheel and little mass to keep the rpms up. I'd like them to drop quickly abd the revs should, but don't. What is wrong with it? This does not happen, or I don't notice it when I am on it hard and shifting at higher ( 5 - 7000 rpm). Note, my car is modified, but has 15%, stock s/c. About 265 hp. It wasn't like this before the rebuild. Might there be some kind of vacuum leak somewhere?

When the engine is cold, this effect is non-existent, but gradually starts as it warms up.

Any ideas?

 

If you have a sprint booster, try it turned off.

 

I don't/wouldn't have the Sprint Booster.

 

I'd just run through all the connections (electrical and vacuum/etc.) that are easily accesible and make sure everything is connected correctly. try resetting your ecu. do you have a stock tune? i'd doubt it considering your making 265 hp on the stock s/c, but it could be the source of the problem. also just run through your spark plugs and check the intake manifold/hose thats after the TB for leaks. thats all i can think of for just diagnostic stuff... are you getting a CEL?

 

I read your other post about he upgraded clutch you have. Is it possible it's just out of adjustment? I'm sure that you got a sprung clutch since you went with a light flywheel (as the stock one is dual-mass). Over-revving while shifting usually indicates it's slipping.

 

I always have a CEL on. Jan (RMW) says its a bad ECU

Taking foot off gas pedal causes engine rpms to increase. This is not related to clutch. It is not related to flywheel. It is not related to how one operates the clutch or throttle Unless you step on clutch and then take foot off gas. Believe me that is NOT what I do. It believe the syndrome is related to electronics or bypass valve or vacuum line or ECU. But there are many connections and lines and stuff in the engine compartment. Surely someone must have a handle on the particular control system elements likely to be causing this.

If I were revving the engine out to 6000 rpm every shift, it would not be noticeable, as the engine revving by itself syndrome is only like a light tap on the throttle, or even delayed lift off the throttle. It does not go high for long, just 1 - 300 rpm for maybe a second, and then drops slooowly.

You'd think with lightweight flywheel the engine rpms would drop like a rock when you take your foot off the gas. That would translate to quick shifts. Unfortunately the syndrome I experience is just the opposite. Much slower shifting and more difficulty in rev matching. Any automatic is much faster than my super powerful mini at normal round town driving speeds. It takes all the joy out of shifting the car and driving smoothly.

 

Hmm... perhaps the accelerator pedal module or throttle body actuator is bad or has a wiring issue?