What the r3v-hang?

[cmybimmer]

Sup guys, over summer I had completed my m50 swap on the e30 and right after, fall semester started so I didnt have much time to work on the small bits of work needed such as cluster lights not working, temp gauge not working, and this annoying rev hang im getting :hitler:.. Ever since the swap I've had this rev hang when I drive. Id let off the gas when in gear (or neutral, but not as bad) and the revs would just sit for a couple seconds, then start to die down. Feels like im driving a damn e46 which = :roll:.

Thing is when I disconnect the maf plug, the rev hang would go away, but would give birth to an idle spasm. Swapped maf's and same thing happened, so it cant be the maf.

Anyway, heres a vid showing what I mean. I know its kindof hard to see/notice it with the angle off and the sun glare in the way, but its the best I can do. In the vid I'd accelerate and then let off the gas right away (in most of the vid) and the times when the revs stay in place is when I let off the gas.



Any ideas?

[AnimalE30]

I had a similar problem when my throttle cable didn't have enough slack in it. Not sure this is your problem if unplugging the MAF fixes it.

Get under the hood, open the throttle all the way by hand, let go of it and confirm it is closing all the way (against the set screw).

[scottinAZ]

check for vacuum leaks. I had a similar problem when the hose from the intake to the ICV was loose. re-connected, and problem solved

[cmybimmer]

^hmmm yeah ill have to take off the intake mani one of these days and inspect all vaccum hoses.

I had a similar problem when my throttle cable didn't have enough slack in it. Not sure this is your problem if unplugging the MAF fixes it.

Get under the hood, open the throttle all the way by hand, let go of it and confirm it is closing all the way (against the set screw).

Yeah that was the first thing I checked. It now has jusr enough slack and the throttle does close enough

[cmybimmer]

Yeah... checked under the hood and couldnt find any obvious vacuum leaks. I checked as many hoses I could while keeping the intake mani on and everything was fine (except for a fuel line that hasnt been clamped all along :loco:)

Could it be my ecu or something? I believe its from an e34, red label 413..

Makes no sense how it doesn't have this problem when I disconnect the maf :-x

[jahnaboi]

It makes sense if the maf is bad. You aren't pulling any codes are you?

[cmybimmer]

Lol about thattt.. I still havent installed an O2 sensor since I have to do some fab work to that crossmember thing. So I DO have a cel as it is now but I figured it was just due to the lack of an O2.

And again, I swapped maf's with a known working one and the problem persisted :/

[giantkeeper]

Read your OBD1 port or stomp test for codes, then proceed

[cmybimmer]

update: today I plugged in the o2 sensor hoping it would kill the rev-hang disease, but it didn't do the trick :(.. It did, however, get rid of the CEL as I thought it would. Motor picks up much smoother now :up:..

I'm running out of idea's here, unless its a problem with my harness adapter that I made :???:.. Sighh

ideas?

[325e10]

I had the same issue with my m52 swap but it was definitely a vacuum leak. I was missing the electronic valve that goes in between the throttle body and the charcoal canister. Not sure if M50 cars had that or not.

[cmybimmer]

yeah I have some sort of valve hooked to the throttle body, but its a possibility I put it in wrong.. I didn't really know if I were to put it before the canister, or after.

I don't think its a vacuum leak, took off the intake manifold a few weeks ago looking for loose hoses and everything looked good to me.

[325e10]

yeah I have some sort of valve hooked to the throttle body, but its a possibility I put it in wrong.. I didn't really know if I were to put it before the canister, or after.

I don't think its a vacuum leak, took off the intake manifold a few weeks ago looking for loose hoses and everything looked good to me.

That's the thing though, all my plumbing was correct and no loose hoses. Just missing that valve, it should go between the charcoal canister and the TB. Make sure it's plugged into the right place on the TB as I had mine originally plugged into the TB warmer line instead of the actual vacuum port. oops.

[cmybimmer]

I will have to investigate tmw.. Do you happen to have a pic of the way it is supposed to be setup?

[Mr.SWISS]

My money is on a sticky throttle butterfly mech. Move with hand and check for a rough spot/bind in linkage.

[cmybimmer]

^I've checked before, but I'll check again. Haven't had the time today to inspect the car, but maybe tomorrow i'll have a small window to pop the hood and check it out. Thanks