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DISCUSSION => General Topics => Topic started by: johna on October 01, 2007, 02:56:45 AM

Title: Starting fault: fluctuating revs
Post by: johna on October 01, 2007, 02:56:45 AM: When I start my M42 powered 1994 E36 318is the revs jump up to about 1500 then drop down to almost stalling speeds, then go up and down a few more times, then stabilise at normal idle speed, about 800rpm.

I have recorded a video (no audio) of a typical start. Please see http://www.youtube.com/watch?v=V9MICx44uHM.

This happens whether the engine is cold or hot and once running there are no idle or running problems whatsoever.

Any ideas on what might be causing the problem?
Title: Starting fault: inconsistent revs
Post by: johna on October 04, 2007, 01:48:41 AM: Does no replies mean that not one of the thousands of members of m42club.com have had this problem and know how it was fixed? Or is it E36 bias? ;)
Title: Starting fault: inconsistent revs
Post by: kowalski on October 04, 2007, 02:03:32 AM: haha that looks like a really weird deal you got going on. an audio clip would be a little more helpful. does it sound like its missing? when it steadies out does it miss at all? does it have power at idle, can it idle along in first gear? will ti stutter if you just floor it in neutral at idle? if you start it let it idle for a bit turn it off and start it again does it do it?
Title: Starting fault: inconsistent revs
Post by: RED IS 91 on October 04, 2007, 08:19:43 AM: I would start with the ICV . Have you checked for vacumn leaks ?? Switched out the ECU maybe ????
How long has it been doing that ?How many miles on your car ?You have to give us more info than a video with no sound .............
good luck
Title: Starting fault: inconsistent revs
Post by: gearheadE30 on October 04, 2007, 08:48:19 AM: Check vacuum leaks first. I have a few that I need to get to and it does almost the exact same thing.
Title: Starting fault: inconsistent revs
Post by: Vladi on October 04, 2007, 12:37:58 PM: I've got a 08/94 1.8iS that does the exact same thing but only with a cold engine and only on the first start. Mine's not that bouncy, does one loop (up,down,up) and stabilises. All hoses are new. Didn't get to try out another ICV though...
Title: Starting fault: inconsistent revs
Post by: johna on October 04, 2007, 04:06:06 PM: It has 160,000km (100,000 miles). I only just bought it a month ago and it has been doing it since I bought it.

It happens on both and hot start but if I keep my foot on the throttle it won't fluctuate.

It only happens at startup. The rest of the time the car idles and drives near perfectly.

If the video had audio you would hear the revs rise and fall and when they fall it sounds like the car is about to stall but then the revs jump up again.

Thanks for the replies!
Title: Starting fault: inconsistent revs
Post by: Febi Guibo on October 04, 2007, 06:13:00 PM: +1 on the ICV...
(I need one too!)
Title: Starting fault: inconsistent revs
Post by: n2motorsports on October 04, 2007, 06:28:51 PM: can the icv be rebuilt easily? like spray some brake cleaner into it? they are pretty costly at around ~150 usd.
Title: Starting fault: inconsistent revs
Post by: johna on October 04, 2007, 10:20:11 PM: If it is a fault with the ICV then wouldn't the idle be bad all of the time, not just at startup?
Title: Starting fault: inconsistent revs
Post by: Febi Guibo on October 04, 2007, 11:32:14 PM: i think the ICV operates differently when the engine is cold vs. after its warmed up
Title: Starting fault: inconsistent revs
Post by: johna on October 05, 2007, 12:25:38 AM: The problem occurs whether the engine is cold or hot.
Title: Starting fault: inconsistent revs
Post by: kowalski on October 05, 2007, 01:27:01 AM: you can test is pretty easily. hook 12 volts up to it and if it shuts/opens then it works. If not i have an extra i'll sell ya.
Title: Starting fault: inconsistent revs
Post by: RED IS 91 on October 05, 2007, 06:23:55 AM: If the icv was bad then it not run well hot or cold .A good cleaning and test maybe all it needs .
Title: Starting fault: inconsistent revs
Post by: Vladi on October 05, 2007, 12:11:28 PM: Quote from: john318isau;35042
If it is a fault with the ICV then wouldn't the idle be bad all of the time, not just at startup?

Probably i'm going to test another ICV next week so if you don't fix it by then i'll come back with a result. ;)
Title: Starting fault: inconsistent revs
Post by: Febi Guibo on October 05, 2007, 02:01:56 PM: Quote from: john318isau;35048
The problem occurs whether the engine is cold or hot.

Really, what I meant was, ICV effecting the idle during the time just after starting up, vs. running....

anyway, I'm going to check mine this weekend too...
Title: Starting fault: inconsistent revs
Post by: n2motorsports on October 05, 2007, 05:19:31 PM: Quote from: RED IS 91;35055
cold .A good cleaning .

please elaborate...what do you recommend cleaning it with?
Title: Starting fault: inconsistent revs
Post by: sheepdog on October 05, 2007, 07:42:06 PM: Vacuum leaks.
First thing to check. Unless you have replaced all of the hoses, you have vacuum leaks.

They will effect it at all temps though usually not enough to nearly kill the engine.
Title: Starting fault: inconsistent revs
Post by: RED IS 91 on October 06, 2007, 05:52:49 AM: Quote from: n2motorsports;35101
please elaborate...what do you recommend cleaning it with?

Take it out and squirt some carb cleaner inside to clean the black crap out if there is any . Then squirt some WD40 for some lubrication . While it's off connect 12 volts to the terminals to see if the valve moves .If it doesn't move then you need a new one . When I did mine I connected two wires from the battery to the ICV ( I just layed the ICV in the trunk and used two short wires from the battery) to see if the valve inside the ICV moved.
Good Luck