High Revving E36

[Vince70]

I’ve got a weird problem with my e36 318 cabriolet which I can’t put my finger on as my E36 decides to increase it revs for no apparent reason.

I’ve now changed the idle control valve and the crankcase breather valve plus the main breather hose And also put another Disa on the car and have checked for air leaks and cleaned up the MAF.

The thing is I’ve adjusted the throttle cable and it sits nicely at 750 rpm when I first start it up and then for no apparent reason starts revving up gradually to 1100 rpm and sometimes when I blip the throttle it drops slightly to 950rpm then creeps back up to 1100 rpm.

[g3org3y]

When my E46 had a few running issues, including rough cold idle, surging revs when coming to a standstill or even cutting out when pulling up to stop, turns out it was the MAF. Interestingly, it never threw a MAF code on the OBD - it was all trim bank stuff. Cleaning didn't help, so just spent some cash and bought a new one (decent OEM Hella - don't buy the cheap Chinese £30 stuff on eBay).

Try unplugging the MAF and run the car to see how it behaves.

Do you have an OBD reader for your E36?

[Touring442]

Clean the throttle body out. These have an alloy unit and a steel disc - this wears a ridge into the alloy and can cause both the disc jamming (does it ever stick?) and an air leak.

P registration could be the old type ICV under the upper manifold, or the later type that bolts to the upper manifold at the front. Cars with ASC have this.

[Vince70]

Thanks for the advice I was just about to give up sorting the problem out and do notice if I take the plastic cover off the top of the throttle body and push it back the revs do drop a bit.

It is a 96 so is the older setup and one thing I haven’t done is take the throttle body off and never really thought of doing that so that’s the first thing I will do on Monday.

[Touring442]

That's the later type with ASC but no air con. The idle control valve is the black plastic thing to the right of the throttle position switch, secured by two allen bolts. I've got a box full at the workshop. Also examine the intake boot for splits.

The TB can be easily removed and the bore cleaned up but don't overdo it as you'll create enough of an air gap to cause an air leak.

[helix402]

Not seen one of those engines for a few years! Used to do so many head gaskets on them I could do them in an hour and a half.

[Elliot2000]

Vince70 said:

I’ve got a weird problem with my e36 318 cabriolet which I can’t put my finger on as my E36 decides to increase it revs for no apparent reason.

I’ve now changed the idle control valve and the crankcase breather valve plus the main breather hose And also put another Disa on the car and have checked for air leaks and cleaned up the MAF.

The thing is I’ve adjusted the throttle cable and it sits nicely at 750 rpm when I first start it up and then for no apparent reason starts revving up gradually to 1100 rpm and sometimes when I blip the throttle it drops slightly to 950rpm then creeps back up to 1100 rpm.

When you say you have adjusted the throttle cable - do you mean you have wound it out until the revs increased? If so, this is not how u want to be doing it- u want the throttle body to snap shut when you are off the Thhrottle pedal so u want it to have a small amount of slack at the end instead of it tugging on it all the time.

[E-bmw]

Elliot2000 said:

Vince70 said:

I’ve got a weird problem with my e36 318 cabriolet which I can’t put my finger on as my E36 decides to increase it revs for no apparent reason.

I’ve now changed the idle control valve and the crankcase breather valve plus the main breather hose And also put another Disa on the car and have checked for air leaks and cleaned up the MAF.

The thing is I’ve adjusted the throttle cable and it sits nicely at 750 rpm when I first start it up and then for no apparent reason starts revving up gradually to 1100 rpm and sometimes when I blip the throttle it drops slightly to 950rpm then creeps back up to 1100 rpm.

When you say you have adjusted the throttle cable - do you mean you have wound it out until the revs increased? If so, this is not how u want to be doing it- u want the throttle body to snap shut when you are off the Thhrottle pedal so u want it to have a small amount of slack at the end instead of it tugging on it all the time.

^^^^Wot 'e said.

Idle adjustment on the throttle cable was a thing of pre-70's cars & is not right on these cars.

Idle is set by the ECU & controlled by the ICV.

[Vince70]

Sorry I should of said I wound the throttle Cable out to give it a bit more slack and fitted a new ICV plus a new CVV valve.
But I will say the throttle pedal does feel a bit stiff compared to my other E36.

[Elliot2000]

If it feels stiff - it’s normally the cable itself and not the throttle body

[Vince70]

I’m still having a bit of trouble with the idle as when warm it’s Still revving at 1100 and I’ve cleaned out the throttle body today but I got my code reader out and got this code.
I haven’t a clue what the second screen means but if it is sensor related I wondered if it’s the oxygen sensor.

[Vince70]

[Elliot2000]

Most likely a big air leak or running very rich - that fault is trying to say it’s tried adjusting the mixture as much as possible and the o2 sensor reading is still too far out so it stops trying.

Could also be down to defective o2 sensor not giving correct readings or air mass meter giving funny readings

[Vince70]

Thanks Elliot for the reply I will have another look tomorrow.
I’ve checked for air leaks and not found anything so far and have tried another secondhand airflow meter so I’m going to most probably try another oxygen sensor which is a bit of a pain as it’s buried underneath the car so I might get someone to fit it for me as I don’t have a set of ramps or a 22mm spanner for the job.

[RUSSELLM]

Don’t forget to listen, look, for exhaust leaks too.

I’ve found O2 sensors to be surprisingly delicate.

[Elliot2000]

Are the vaccuum hoses going to the fuel regulator ok?

Have you checked your breather is working?

Disa valves can often cause a leak too

Edited by Elliot2000 on Wednesday 10th June 11:18

[Vince70]

Thanks I’ve not checked all the hoses yet but will tomorrow I thought I would give it a break today as finished tidying up the wiring on a set of spotlights I fitted on my old R50 and then it started raining.

I know I’m clutching at straws but I have an old bottle of Cataclean indoors and was thinking of chucking it in the tank and giving it an Italian tuneup and see if it makes any difference.

The shame of it is the car is nigh immaculate and low mileage but it’s driving me insane at the moment.

[Elliot2000]

Looking at your engine bay picture - it doesn’t oook like the vac hoses are attached to anything on the on the fuel results or, might be just the photo tho

[Touring442]

The manifold vac outlet is just there on the right hand hose end.

[Vince70]

I forgot to say the vacuum hose is connected and the car runs fine apart from the revving issue.

I took the car for a long drive today and it doesn’t seem to be using any oil or coolant but it did overheat last year so changed the complete cooling system as it needed a new viscous fan but I think the head gasket is okay as it runs without a misfire and hasn’t got any mayo in the oil or oil in the coolant plus the heater is lovely and toasty and the temperature gauge sits perfectly in the middle and doesn’t move anywhere near the red.

Also if I disconnect the wiring from the airflow meter the revs drop for a split second and the revs still go back up to 1100 rpm but when the car is cold it sits at a perfect 750rpm.

Edited by Vince70 on Saturday 13th June 16:08