Author Topic: Intermittent Idle Bounce (Read 5586 times)

ClassicSkril · « **on:** December 03, 2010, 03:46:51 AM »

My car has been idling strange since I purchased it a while back. Got all the belts replaced, and did the fuel filter, and in addition the mechanic said I did not have a vac leak. Several hoses have been replace since then and the car still idles strange about every other time I drive it. It drops to 500rpm, then after a second it bounces up to a thousand. Any thoughts? It resurfaces, sometimes I don't have this issue, then it returns. Also I have no power loss issues when driving.

91 318IS

DesktopDave · « **Reply #1 on:** December 03, 2010, 07:04:02 AM »

I'd clean & test the idle control valve to start. Might be that. I'd also double-check the main intake hose for cracks and the hoses under the main intake tube. Did your mechanic do any tests, like a propane gas cylinder, or did he just do a good look-over? I've found that those hoses really like to leak, and it's difficult to find leaks.

ClassicSkril · « **Reply #2 on:** December 03, 2010, 01:14:06 PM »

Thanks for the tips I will definitely try that. I have heard people say the main intake hose can be cracked and still look brand new. I did replace a small hose beneath it which was cracked. The previous owner had a ghetto short ram setup which caused the intake hose to sag and the MAF to have a downward angle which isnt good. But yea my mechanic said he did the spray test and there isnt a vacum leak. where on the intake hose does it normally crack?

DesktopDave · « **Reply #3 on:** December 03, 2010, 10:49:49 PM »

Mine cracked around the hose clamps on both the AFM and the TB. I used a little black RTV and electrical tape to patch it temporarily a year or so ago. You can test the ICV by feeling if it vibrates when the motor is running. I've also tested it by pulling the harness & using a 9v battery with flying leads.

A good penetrating oil like SeaFoam Deep Creep or PB Blaster should clean it up nicely if it's sticking. Try to keep the oil in the valve body though, I've heard it's not good to get it into the motor mechanism. I brought one back on an M20 eta by soaking the valve body with Deep Creep, stood it on the valve body (motor end up) and let it dry pretty well before re-installing it.

ClassicSkril · « **Reply #4 on:** December 04, 2010, 01:19:33 PM »

thank you very much for all the suggestions. I will try these and see how things are looking

ClassicSkril · « **Reply #5 on:** December 07, 2010, 04:31:19 AM »

I did some searches on write-ups for removing and cleaning the icv, as I have never done this. The entire intake manifold must be removed correct?

bmwm42 · « **Reply #6 on:** December 07, 2010, 11:13:27 AM »

you dont have to remove the manifold all you have to do is remove the 10mm bolt and it comes right out just disconnet the two hoses that are attached to it and clean away with you cleaner of choice its a very simple job

ClassicSkril · « **Reply #7 on:** December 07, 2010, 02:39:26 PM »

Ok thanks. And it is located under the manifold towards the fire wall if I read correctly?

bmwm42 · « **Reply #8 on:** December 07, 2010, 08:15:24 PM »

its not under the manifold its behind it you should be able to see it with the hood open if you look on the back of the the intake manifold there is a hose connected to it and that hose connects to the icv

ClassicSkril · « **Reply #9 on:** December 07, 2010, 11:34:30 PM »

I wish I could find some pictures on here of this. I'm sure there are some just haven't had any luck.

ClassicSkril · « **Reply #10 on:** December 08, 2010, 01:42:05 PM »

I removed it last night. It was a little awkward due to the tight space but I managed. It was dirty, but what was worse is there is a split at the end of the tube that connects to the bottom of the ICV. So needless to say I think removing the manifold will be next to replace all my lines under there, if my idle doesn't improve

bmwm42 · « **Reply #11 on:** December 08, 2010, 02:02:33 PM »

fyi you dont have to remove the manifold i didnt just remove the intake boot and you will have nice access to all the lines i bought 19/32 hose from auto zone and fitted hose from carquest for like 7 bucks that connects to the bottom of the icv and used the existing plastic tees to make things fit again total investment was like 15 bucks to fix the mess

ClassicSkril · « **Reply #12 on:** December 08, 2010, 07:00:24 PM »

Quote from: bmwm42;99437

fyi you dont have to remove the manifold i didnt just remove the intake boot and you will have nice access to all the lines i bought 19/32 hose from auto zone and fitted hose from carquest for like 7 bucks that connects to the bottom of the icv and used the existing plastic tees to make things fit again total investment was like 15 bucks to fix the mess

whoa nice. so to replace that lower hose I can actually do with non oem hoses? and without the manifold being removed? the only write-ups I have seen were with it off

ClassicSkril · « **Reply #13 on:** December 15, 2010, 09:00:25 PM »

I cleaned my icv and I am still having idle issues. Is it likely to be a vaccum line issue or could it be something totally different like my alternator?

MrAlan · « **Reply #14 on:** December 16, 2010, 02:43:43 PM »

Im having a similar problem with my 95 318is although its not intermitent and havent solved it yet, however these are the things ive looked at so far
check your airflow meter ( AFM) you can take that off and make sure the flaps opening freely but if its an electrical fault youll need to replace it. The other thing is the throttle position sensor, located on the throttle body this tells your ecu how much fuel to dump and may be sending the wrong signal? 1 more option is the Lambda sensor located on the exhaust under the car, this is another fuel/air regulator and that too could be worth checking.
Hope that helps