Help! Throttle problems

[Atif]

Hi

I'm having major problems with my C180 (97/P), manual, saloon.

On cold starts it starts but then cuts off. Second time around it starts but then idles to a point where at times it cuts out or remains on the borderline of cutting out unless i rev the engine.

I had the car serviced (by a local garage) and since then I have started to experience a lack of power - especially whilst the car/engine is cold. When driving of, the revs dont go above 2500 and it feels as if the car cant make its mind up about moving any faster (jery ride). I have tried to press the accelerater all the way down but that has no affect whatsoever.

The mechanic has cleaned the MAS and throttle body. He thinks it might be the fuel filter (near the petrol tank?).

It seems to be getting worse since i have to leave the car running to warm it up. Even when i am doing 70 on a motorway and want to go a bit faster it at times slows down. Using the kickdown just gets the revs to decrease rather than increase

Any pointers/advice will be appreciated for when i see the mechanic (later today).

Thanks

 

[grober]

Certainly sounds like fuel starvation. When was the fuel filter changed last. New Hengst filter only about £20 from EuroCarParts.

 

[Atif]

Grober - thanks for your suggestion. I'll bear that in mind when i see the mechanic later.

 

[grober]

Temp sensor?

There are 2 temperature sensors which might be causing the problem of poor running when cold. 1. is the coolant temperature sensor located on the thermostat housing at the front of the engine normally furthest left looking from the front.(possible) 2. the inlet air temperature sensor on the air duct between the MAS and the inlet manifold at the manifold end.(unlikely) Other possibility might be the LAMBDA sensor on the exhaust manifold.(possible) they all influence fuel mixture control to varying degrees. Then there is the perennial favorite the MAS sensor (likely) but ruled out since you said its been checked out.

 

[nickmann]

Throttle position sensor (near the brake fluid reservoir)

 

[grober]

Electronic throttle

Throttle position sensor (near the brake fluid reservoir)

Distinct possibility. I had forgotton the later models had an electronic throttle. Comes from driving a w124 I guess.

 

[Atif]

Throttle position sensor or MAS?

Hi guys

Re the "sensor" problem - on my way home last night i disconnected the MAS (I believe this is the plug attached to a part of the air intake/filter) - the car seemed to behave alot better than with it connected!!!

This morning i left it unconnected and the car didnt cut out like it usually does first thing. Plus i had power and was able to accelerate whilst the engine was cold. The slight problem was when standing in traffic the revs would be bouncing around a bit (between 500-1000) and on a couple of occasions when pulling away there is a slight hesitation in acceleration.

Am i correct in thinking it is the MAS - this looked clean (visual inspection) and the mechanic only cleaned it using compressed air.

A couple of Qs - is it safe to drive with it unplugged? Is it worth cleaning (and with what) or is it best to replace altogether (costs?) new/second hand?

Thanks for your help.

 

[nickmann]

Yes, that is the MAS. I think you have correctly isolated it as the cause. You can try cleaning it with carb cleaner or brake cleaner - presently it is broken so you cannot make it any worse! I drove mine unplugged for a short test with no ill effects. I'm sure the ECU has some defulat settings to use in the scenario where the signals from the MAS are out of range, or absent/

A replacement unit is about £230, but do a search as someone recently posted that they obtained just the innards for a fraction of that price.

 

[Atif]

Thanks Nick

I'll be speaking to my mate the mechanic later today to see if he can get me some prices. He suggested that we hook the car on to the pc to check the error codes (£40+ vat). Is this still worth doing or should i just get the cleaning kit out first?

 

[grober]

People have used lots of solvents for this with mixed success but some form of degreaser e. g. carb cleaner which is not too corrosive would be best. Another post http://www.mbclub.co.uk/forums/showthread.php?t=25019 suggested electrical component cleaner which is fine just make sure it doesn't have any lubricant in it also as that would just make things worse. Have a look for some other posts on MAF or MAS on the forum.See this recent post for cheaper replacement details. you will have to determine the exact unit for your model. http://www.mbclub.co.uk/forums/showthread.php?p=233656#post233656 and the pierburg web site http://www.msi-motor-service.com/ks/en/kataloge/luftver_en.asp

 

[Bazzle]

Do NOT use compressed air. Only clean with brake clean and shake dry.

Bazzle

 

[nickmann]

£47 to read the error codes?? I'd find another mate.

 

[Atif]

Update:

I stopped off at halfords and picked up a torx kit (@ £9). I was also about to get some brake/clutch fluid but was not sure if it has any lubricants in it - so i asked the assistance who wasnt sure but suggested an alternative - a spray to clean electronics (plugs etc) @ £4.

Got home, took the MAS/MAF apart (2 screws - thanks Graemer for the pics/threads). Cleaned it a few times with the spray and let dry out. The sensor has the "electrode" on the main body but also has a few pins (towards it tip) which seemed to have been covered with dirt. Made sure everything was clean and dry and replaced it.

Gave it a test drive and it was alot better but the car was warm so couldnt notice all that.

This morning - NO CUT OUT and it drives nearly like new.


Thank you to all those who have helped and the forum too. I must have saved at least a few pounds!!! Will keep an eye on it just in case it needs to be replaced at some stage.

To think that my first mechanic recommended the throttle body (£400 quote).

 

[grober]

Result!

RESULT! hope this cures it on a permanent basis but if not the Pierberg replacement would be easy now you know how to do it. Might be worth changing your air filter now if its dirty?
Credit to Steve Perry for posting his HOW TO. I'm sure he would appreciate a PM sayin so.