farisa

Hi guys,

I'm new here. Actually, I've problem with my m111 engine where the idle speed couldn't maintained at the desired speed (mean, the speed is not stable). Basically, I can feel that the speed like ramping up and down say for around 0 to 400 rpm differences.

Anybody has any idea regarding this issue?

Thanks

Glyn M Ruck

Man oh man - this can be many things. Have you got an OBDII scanner & checked for codes? It can be anything from O2 sensors cycling too slowly to the throttle plate actuator in the throttle body.

LILBENZ230

Hey Glen, my car has done this a couple of times in the past week as well. I haven't scanned for stored codes, though. It's happened just after start-up, while in gear, the car will feel like it almost stalls then pulls the RPMs up then almost stalls again - repetitive - for a few seconds but then it goes away. I chalked it up to O2 sensors. At 66,500 miles. I'll be watching this thread!

farisa

Hi Glyn,

Thanks for the reply.

Checked the fault code where it appeared no. 021 (Idle speed control in emergency operation). Beside, I've changed the other set of the throttle body, the result was the same where idle speed kept ramping up and down..

Glyn, what did you mean by O2 sensors cycling too slow? How could I check this?

Glyn M Ruck

Matt - when the car is cold in open loop any number of tuning issues can cause it to stumble including O2 sensors. Then the auto idle circuit takes over & tries to correct & stop it from stalling. You need to watch plugs, coils, wires, temp sender unit that calls for mixture enrichment etc. Chuck a bottle of Techron concentrate in the tank. You might just have a slightly fouled injector. On Phils car with M271 it was the throttle actuator. Check for stored codes.

Glyn M Ruck

Your code could not have been a P0021 even though the explanation is correct for what you are experiencing. 0121 & 0221 are throttle position sensor trouble codes

P0021 = "A" Camshaft Position - Timing Over-Advanced or
System Performance (Bank 2)

You don't have a Bank 2 to have an inlet cam problem - Check the code again.

You cannot DIY check an O2 sensor's cycle time. What mileage have your O2 sensors done? They have a design life of about 80,000 miles before they start to cycle too slowly. Engine stumble is a typical of O2 sensors but can be many other things - see my reply to Matt below. Sooner or later they will trigger a code. Only answer is to replace them.

Please check codes again. I'm hoping it will have stored a code that gives us some idea of what to check first. e.g. low engine temperature like a 0128 - Shot thermostat. The we know the car is likely going to trigger a 125 which means it's staying in open loop & the idle controller is having to compensate for this.

Good luck

MOBC200K

I've come across this before only seemed to happen when i was reversing but did happen once or twice taking off. Only the other day when i started the car i could feel a slight roughness like a misfire just not as bad. I'll be keeping my eyes on this thread

LILBENZ230

So I'm not alone here. IIRC, Phil's C230 had a CEL on. Or maybe that was for a different issue of his to do with the EECS code when he had that leaky fuel filler neck (just like my car did). Also, Glyn, my car was not cold when this happened. It had only been parked for about 15 minutes and the engine was still very close to normal operating temp.

My car has no stored codes. I have been using Texaco with Techron and three tanks ago ran some Techron concentrate.

Glyn M Ruck

Oh Boy! - this is needle in a haystack stuff - we'll work it out. We might need some trial & error here. Thanks for clarifying your situation Matt. Phil's car had 2 problems. The EECS nonesense & then the erratic idle which was the throttle plate actuator. Replaced throttle body & problem was gone.

LILBENZ230

My car has only did this a couple of times and is mostly fine. The RPM just occasionally seems to dip too low and the car shudders and pulls it back up. Sometimes it's a single time, sometimes it will do it a few times.. but neither happens on a regular basis. I suppose I won't worry about this till it becomes serious. My car is very reliable and never lets me down.