When I knock my car (UK turbo 2000) out of gear coming to lights or junction I noticed the RPM drops to about 300 then returns to its normal 700 - 800 RPM at idle. I took the MAF sensor out on Saturday and cleaned it with Carb cleaner. I cleaned the pins and the connecting plug too for good measure. I put all back together, reset the ECU then drove the car about 30 miles. This didn't totally cure the problem, but the mesh in front of the MAF was visibly dirty and there was some evidence of contamintation on the filament itself which the carb cleaner removed.

My revs now 'bounce' at idle, swinging from 500RPM to 1000RPM. I dont think I could have broken the filament in the MAF by squirting a liquid onto it surely??

I have checked my SECS unit which reports no faults and the CEL light is not on. I spoke to my dealer this morning who said not to go swapping parts out until the CEL comes on - as this could be an expensive way to eliminate the fault.

Apart from trying another MAF which I dont have, is there any other areas I should be looking at for the unusual dipping in revs or the swinging revs. Nothing else has been cleaned, changed or disturbed on the car.

I would assume the ECU measures the reisitance of the filament, only when this is out of tolereance will it map in a safe value and put on the CEL. I dont see how cleaning it could have damaged it.....

TT

 

MAF failure rarely puts the CEL on as it doesn't fail outside of the working range to the ECU doesn't realise it has failed.

the 99-00 is a fairly sensitive MAf sensor and you are unlikely to get away with cleaning it.. that in itself can damage it.. time for a new one.

The dealer knows very little about MAF failures if that is there attitude..
Although at least they didn't try and sell you anything..

Simon

 

the other option is the iscv - idle speed control valve - near the throttle body, this can also get bunged up with gunk and I think this is more likely to cause this issue, its also easy to clean, but first try disconnect the maf (you get a secs so can easily reset the cel) then drive gently without the maf and see what that does. It will easily point the fault out

 

99-00 doesn't have an idle valve.. it uses a stepper motor..

 

well that thingy then

I thought they all had the same name

I think your "stepper motor" is out of step then

 

lol. . they sometimes get out of step on after market ecus.. but not generally a problem on standard ecu and then when out of step the car won't start rather than idling wrongly.

99% sure it will be the MAF sensor.

The fact that cleaning it altered it kind of says it all.

Simon

 

I'd also try and ECU reset just to be sure. But if you've a my99/00 car and your MAF doesn't have a green spot on it (by one of screw holes) then replace it regardless (IMHO).

Richard

 

whats the green spot for ?

 

Green spot ones are the revised type and supposedly more robust. I replaced my MAF sensor as a service item to a green spot one.

I thought if you think you have a faulty MAF on 99/00 cars if the engine still runs without the MAF then its definately gone - it should stall without a serviceable MAF.

 

Don't forget to drive off boost until you replace it, or you will be replacing something more expensive than the £70.00 MAF.