Bouncing throttle when coming off power (around 1 - 1.5k rpm)

[Dzdimi14]

I am having a weird problem when I come off the throttle in second or third gear (usually around 25-30 mph but can happen at faster speeds) where the revs start bouncing from 1K to 1.3-1.5k the moment the tach lowers down to that region when slowing down. I have a 89' 325i Automatic, so the only way I can slow down comfortably and safely is by shifting into neutral. While in neutral I can still hear the revs bouncing and they don't settle down back to idle until I have completely stopped for a second or two. I am guessing a vacuum leak is part of the issue since I have been doing a lot of work to the car which has required me to take off the intake manifold like 4 times in the past few months. I am sorting out a smoke test at the moment but I was wondering if this could be a sensor issue. I have read about people needing to re adjust their tps? could that be part of the problem?

[82eye]

I am having a weird problem when I come off the throttle in second or third gear (usually around 25-30 mph but can happen at faster speeds) where the revs start bouncing from 1K to 1.3-1.5k the moment the tach lowers down to that region when slowing down. I have a 89' 325i Automatic, so the only way I can slow down comfortably and safely is by shifting into neutral. While in neutral I can still hear the revs bouncing and they don't settle down back to idle until I have completely stopped for a second or two. I am guessing a vacuum leak is part of the issue since I have been doing a lot of work to the car which has required me to take off the intake manifold like 4 times in the past few months. I am sorting out a smoke test at the moment but I was wondering if this could be a sensor issue. I have read about people needing to re adjust their tps? could that be part of the problem?

tps wouldn't make a bounce as much as a consistent wrong. you're probably right on the vacuum leaks. possible icv issue, but work on the cheap stuff first.

[MR 325]

I would definitely start with a smoke test.

Also definitely check the functionality and adjustment of the TPS. Iff you haven't before, it doesn't hurt to clean your ICV.

[ZeKahr]

I am having a weird problem when I come off the throttle in second or third gear (usually around 25-30 mph but can happen at faster speeds) where the revs start bouncing from 1K to 1.3-1.5k the moment the tach lowers down to that region when slowing down. I have a 89' 325i Automatic, so the only way I can slow down comfortably and safely is by shifting into neutral. While in neutral I can still hear the revs bouncing and they don't settle down back to idle until I have completely stopped for a second or two. I am guessing a vacuum leak is part of the issue since I have been doing a lot of work to the car which has required me to take off the intake manifold like 4 times in the past few months. I am sorting out a smoke test at the moment but I was wondering if this could be a sensor issue. I have read about people needing to re adjust their tps? could that be part of the problem?

If a smoke test doesn't reveal your vacuum leak, check your manifold vacuum level. I have almost the same car as you (1989 325iX auto) and it has pretty similar symptoms: rev bouncing around 1000-1500 RPM on deceleration, running rich at idle, rough but steady 500 RPM idle when fully warmed up. it has pretty low vacuum (15 in Hg in Park, 14 in reverse, 13-14 in drive - all readings steady). Ideal vacuum level should be closer to 17-22 in Hg. Based on those readings, I could have slightly low compression, cam timing off, or a vac leak at the injector seals and/or manifold gaskets

[Dzdimi14]

After driving the car around a bit more I'm finding this to be an intermittent problem. Would an intake leak cause this to only happen like 40% of the time I'm driving? I thought that would be a more constant issue.