90' 320 convertible - Revving crazy high at idle

Post Thu Jul 26, 2018 1:37 pm

Hello,

Just trying to get to the bottom of a problem and wondered if anyone else had experienced it?

Occasionally when starting up the engine will default to around about 3500rpm at idle... sometimes I can fix it by turning it off and on again a few times, other times I have to drive whilst it's doing it, which is a problem as when I dip the clutch the engine is screaming.

Post Thu Jul 26, 2018 1:57 pm

ECU reset crack in take boot, other then that don't have a clue. Auto or manual?

Post Thu Jul 26, 2018 2:02 pm

Ah thanks! What do you mean by "crack in take boot"? It's a manual and has had various electrical niggles in the past. One mechanic suspected a vacuum leak, but because it's intermittent, he wasn't sold on that. Do you know how to reset the ECU?

Post Thu Jul 26, 2018 3:19 pm

i had a similar issue, when i put the icv on the wrong way around .
Check its working properly , could be stuck open. remove and clean.
dayve means the intake boot between the air box/air control valve and throttle body if split will cause revving.
in engine bay by inlet manifold area biggest rubber hose you can see. often cracks.

Post Thu Jul 26, 2018 3:22 pm

a. f m = air flow meter .... air control valve

icv = idle control valve

check out wiki on here for more info

Post Thu Jul 26, 2018 3:39 pm

Guys, thank you very much! This is very helpful! Had a look at the wiki but I couldn't see much about problems/problem solving in it. The one thing that I don't understand is why it's so intermittent? Some days the care will run smoothly with no faults... then it'll randomly just start up and over rev like mad. I can't seem to work out a pattern either for example cold start, after a long run, after town drive or motorway drive etc...

I'll let you all know if I get to the bottom of it!

Post Thu Jul 26, 2018 3:47 pm

Intake boot the large rubber bit from air filter box, I had an issue as it split as I also had an issue when I had a retard moment and didn't tighten up the jubilee clip.......

Reseting ECU disconnect batter for 30 mins,

Clean the ICV in petrol then refit.

Post Thu Jul 26, 2018 3:47 pm

Intake boot the large rubber bit from air filter box, I had an issue as it split as I also had an issue when I had a retard moment and didn't tighten up the jubilee clip.......

Reseting ECU disconnect batter for 30 mins,

Clean the ICV in petrol then refit.

Post Thu Jul 26, 2018 8:37 pm

Have you checked the accelerator cable allows the throttle to fully close?

Post Thu Jul 26, 2018 8:43 pm

DHFiS wrote:Have you checked the accelerator cable allows the throttle to fully close?

Yea that was one of my first thoughts. It's engaging properly and then dropping back into place. It's an intermittent problem which happens every now and again, but has become more common in the last month.

Cheers for all the input though guys! I've got it booked into a garage on Monday, but he is very much a nuts and bolts mechanic and basically said if it doesn't happen whilst he has the car, then he can't hunt down the issue.... which is a bit of a worry!

Post Fri Jul 27, 2018 9:05 am

could Also be the blue temperature sender or wiring from it. that tell the ecu the temp of the engine coolant , obviously the colder the ecu is being told the temp is the faster it will idle.

another thought ishave you cleaned out the throttle body inside they get gummed up and could occasionally stick in a open position.
Also you got the tps throttle position sensor. which is basically a switch telling the ecu if your throttle is closed or wide open ., again look at wiki , tell how to test and or adjust. if its an intermittent fault mechanic won,t find it unless hes got a code reader might help , but our cars are obd1 , so a standard scanned wont work on it .most cars are obd2 (obdII) iirc post 96.

Post Mon Sep 03, 2018 5:18 pm

UPDATE - I had a an auto electrician take a look at it and it looks like its a broken IDLE CONTROL VALVE. It's jamming open. That was also combined with the fact a dodgy mechanic had attempted to fix my previous idling problem by resetting the idle screw so it was out of sync with the idle switch, which confused the Air flow meter.

So hopefully i'll get it running sweet again!

Post Mon Sep 03, 2018 10:55 pm

icv , don,t normally break just sticks , need s a good clean.

yes to second part. if you screw in the throttle stop too much it, (to increase idle ) stops the icv working
found this out in my errors.
As the icv gets its signal to operate only if TPS is adjusted correctly and tell the ecu the engine is at idle.

the more you learn the more you realize how much you dont know...... grasshopper

Post Mon Sep 03, 2018 11:04 pm

Soak the ICV in petrol then refit.

Post Tue Sep 04, 2018 11:25 am

Carburetor cleaner is the one!

Paul

Post Tue Sep 04, 2018 9:15 pm

yep i agree , clean with carb cleaner, shake it should rattle , then lub lightly with diesel
l