Bouncing high idle issue

[BoxDriver86]

1986 325es, m50tu swap with S50 cams and turner chip.

So I had my swap in and running great until my pressure plate exploded. Since I couldn't get the trans out separately, I dropped the subframe with the motor and trans all together to fix it. Now I put it all back together and I have a crazy idle issue.

It will start right up and idle up and down from 1500 to 3500rpm. When I disconnect the MAF, the idle will smooth out.

Things I have checked so far:
-vacuum - smoke test was clean
-icv - cleaned and tested, vibrates when running
-MAF - cleaned and tested
-Wiring - all looks great, like I said it ran perfect before and nothing was done to the wiring in the process of taking the motor back out

Has anyone seen this before? My search yielded only one other issue and of course the OP never reported back to state whether or not the issue was resolved.

I appreciate any help you guys may have. Since I suck at internet, I have posted a link to a youtube video below. It was on my phone and I am working solo so I apologize for the quality.

Link: https://www.youtube.com/watch?v=KB0M...ature=youtu.be

Thanks in advance! This is literally the last thing I have to do before having the exhaust welded back up and installing AC.

[Rdreas]

1986 325es, m50tu swap with S50 cams and turner chip.

So I had my swap in and running great until my pressure plate exploded. Since I couldn't get the trans out separately, I dropped the subframe with the motor and trans all together to fix it. Now I put it all back together and I have a crazy idle issue.

It will start right up and idle up and down from 1500 to 3500rpm. When I disconnect the MAF, the idle will smooth out.

Things I have checked so far:
-vacuum - smoke test was clean
-icv - cleaned and tested, vibrates when running
-MAF - cleaned and tested
-Wiring - all looks great, like I said it ran perfect before and nothing was done to the wiring in the process of taking the motor back out

Has anyone seen this before? My search yielded only one other issue and of course the OP never reported back to state whether or not the issue was resolved.

I appreciate any help you guys may have. Since I suck at internet, I have posted a link to a youtube video below. It was on my phone and I am working solo so I apologize for the quality.

Link: https://www.youtube.com/watch?v=KB0M...ature=youtu.be

Thanks in advance! This is literally the last thing I have to do before having the exhaust welded back up and installing AC.

Holy crap man this is the same fucking problem I am experiencing. Originally I thought it was a vacuum leak or a bad icv. I cleaned my icv and replaced my hoses and I still have the issue. Some of the results i turned up on my search said Cam position sensor so I might check mine, I will keep you posted if I figure it out. If you fix it please post what you did I would be very interested.

Edit: I have a 84 325e m50tu swap with ebay headers and a trm chip

[BoxDriver86]

For the searchers: Problem was fixed. Turns out it was a vacuum leak after all. The ICV was on a weird bind in its rubber holder which pulled the turkey neck hose ever so slightly out of the back of the throttle body and cracked the plastic connector. I had a spare, swapped them out and all is good.

[Nick_S]

I'm going to double check mine. I just took my intake manifold off to fix my blower motor and when I put it all back together, it runs fine but has a definite bounce in the idle. Not as extreme as the video above but noticable and annoying. I'll have to check my ICV and the hoses.

[glucklich21]

Holy crap man this is the same fucking problem I am experiencing. Originally I thought it was a vacuum leak or a bad icv. I cleaned my icv and replaced my hoses and I still have the issue. Some of the results i turned up on my search said Cam position sensor so I might check mine, I will keep you posted if I figure it out. If you fix it please post what you did I would be very interested.

Edit: I have a 84 325e m50tu swap with ebay headers and a trm chip

Something you guys may want to check is that all the ground wires going to each one of those sensors is good. That literally had me chasing ghosts for a year. I replaced every sensor on my S50, literally, in the hopes it would stop it's erratic idle. Some days it started up as if nothing was wrong, another would do the idles above. I finally broke down and brought it to a specialty shop where they hooked it up to an actual BMW diagnostic computer. That revealed my ground wires leading to the ICV and MAF somewhere in the harness were fucked. Ran new ground wires and it was perfect.

May not be the problem, but just a thought.

[Nick_S]

FYI. I have been dealing with some similar idle issues like I stated earlier. Tossed a different TPS on last night and it seems to have sorted it out. I'm told they rarely fail but it seems mine was the issue.

[Rdreas]

FYI. I have been dealing with some similar idle issues like I stated earlier. Tossed a different TPS on last night and it seems to have sorted it out. I'm told they rarely fail but it seems mine was the issue.

I ended up putting a new O-ring on the ccv and vacuum line plugs over the bottom ports of the throttle body and now I have a steady 1k idle which is much better then what i had.