revving up on its own?

[Need4Speed1299]

Fixed.

[red325]

I have an 87 325e with a new ICV. Once the engine gets warmed up and I drive it around for a little bit, it decides to rev up to about 4k on its own. Once i drive for a little bit more it will go back to normal. Its almost like cruise control except it kicks on by itself and doesnt turn off until it cools off a bit. Also my car is starting hard, maybe thats related?

One day, when I was starting up my car to head home, my revs climbed just like yours did. The check engine light came on, but I thought the revs would settle down so I didn't turn off the car immediately. Once they got up past 3k I got worried and shut it off. I punched the gas a few times to make sure the accelerator wasn't stuck or catching on anything. Started it again, same thing happened, check engine light, revs climbing, but I shut the car off before the revs could get to 2500. Third try it happened again. Fourth time it started fine and drove it home. Drove it home and haven't had a problem since. This was about a month ago.

I don't know what to tell you, mine just kind of fixed itself. I'm not sure if we have the same exact problem, but I think it's pretty close.

[jlevie]

You have a new ICV, which means that there are three possible causes of this problem. One would be intake leaks, another would be a bad idle control module (ICM), and the last would be a sticking throttle cable or throttle body. With the other symptom being hard starting, the chances of intake leaks being a player is very high. The definitive diagnostic for intake leaks is to have the intake, crankcase, and evap control system smoke tested.

After eliminating intake leaks and a sticky throttle cable/body as possibilities, the ICM becomes the prime suspect.

[slo325i]

Mine did this when I accidentally plugged into the wrong coolant temp sensors. What should have been plugged into the blue, it was plugged in the brown. When the car warmed up, it stayed at 4k idle... I dunno if this'll help tho...

[borise30]

jlevie can you run us through the smoke test methodology?

Please as I for one are not familiar with it!

[jlevie]

A smoke test requires a special machine. The process is to pressurize the intake, crank case, and evap control system in turn with smoke laden air. Any leaks become immediately apparent.

[emi325i]

I had a piece of plastic break off and fly into the throttle body. It did the same thing.. it would accelerate on its own from time to time until the plastic piece made its way into cyl#6.

[Need4Speed1299]

I had a piece of plastic break off and fly into the throttle body. It did the same thing.. it would accelerate on its own from time to time until the plastic piece made its way into cyl#6.

That doesnt sound good at all. It seems to have gone away now. What a strange problem.

[Snowmann]

You have a new ICV, which means that there are three possible causes of this problem. One would be intake leaks, another would be a bad idle control module (ICM), and the last would be a sticking throttle cable or throttle body. With the other symptom being hard starting, the chances of intake leaks being a player is very high. The definitive diagnostic for intake leaks is to have the intake, crankcase, and evap control system smoke tested.

After eliminating intake leaks and a sticky throttle cable/body as possibilities, the ICM becomes the prime suspect.

Where is this ICM? I've got a 173 ecu, brand new ICV, brand new coolant temp sensor, and the engine was just gone through and has all new gaskets etc... I checked the notorious spots for air leaks and I've got nothing... Any help would be appriciated... In my case I'm thinking it HAS to be electronic related as it does it immediatly after coming out of the cold start-up loop.

And on a cold morning etc. I can make it go away by getting the car cool again, but once it pops above the blue area on the temp gauge its back into the climbing high revs...

[Need4Speed1299]

The ICM is in the glove box by the ecu. I am pretty sure mine is bad, causing it to rev up on its own.

So my car starts really hard also. When I unplug the ICV it starts up great. ICM again??

[jlevie]

Where is this ICM? I've got a 173 ecu, brand new ICV, brand new coolant temp sensor, and the engine was just gone through and has all new gaskets etc... I checked the notorious spots for air leaks and I've got nothing... Any help would be appriciated... In my case I'm thinking it HAS to be electronic related as it does it immediatly after coming out of the cold start-up loop.

And on a cold morning etc. I can make it go away by getting the car cool again, but once it pops above the blue area on the temp gauge its back into the climbing high revs...

A car that has a 153 or later DME doesn't have an ICM. Beginning with Motronic 1.1 the functions of the ICM were integrated into the DME.

Having this happen when the DME shifts to closed loop mode would suggest an intake leak, bad O2 sensor, or bad AFM (given the parts recently replaced).

In addition to the obvious hoses, intake leaks can be from:

1) intake manifold gaskets
2) injector seals
3) evap control system
4) dip stick o-rings
5) oil filler cap seal
6) valve cover gaskets
7) oil return tube seals
8) brake booster

A smoke test of the intake, crank case, and evap control system is the best diagnostic for intake leaks.

[Snowmann]

Well I will say, that this was a 153 car, I had the surging idle problems back in the day and got a 173 ecu to remedy that.

The car ran fine with the 173 ecu, and now after pulling the engine I've got this problem...


I've also got a 1222 code, and my A/F ratio gauge is showing an extremmely lean mixture at idle...

I'll have to probably find someone with a smoke machine to do this...

[Need4Speed1299]

Good info though.