Hesitant acceleration

[bibamus]

Well, my "new" 1997 C180 Elegance Auto arrived on Friday, and on the whole, I am very impressed with it. Just a couple of minor niggles.

1. When starting the engine from cold ( it always starts first time) it fires then the revs drop to just under 500 rpm then build up again. When its warm, no such problem. Is this something I should be concerned about, if so, what could cause it. Normal rpm is about 700 or just below when in D.

2. When accelerating hard, ( foot buried in the carpet) sometimes it seems to hesitate a bit up to about 4500 rpm then the power seems to come back and the car surges forward. This doesnt happen all the time and seems to be more noticeable in third. It doesnt seem to happen using a more moderate right foot.

Car has done 94500 miles, MBSH up to 64000 then an indie. Last service was 88000.

Other than that ( and a query posted in the Electrical forum) the car runs and sound like new.

Allan

 

[jberks]

Hesitation could be the MAS or the o2 sensor - best to get a diagnostic done.

 

[bibamus]

Just tried it out again to try and pin down when the hesitation happens. I only seem to notice it when the throttle is wide open, in all gears but mostly in 2 and 3, if I let the pedal up a bit, it starts to pick up better. Today, it accelerated slowly and wouldnt rev over 4000. If I drive it using small throttle openings it seems fine and runs very well and will rev over 5000 easily. Reading all the relevant posts it looks like the MAF may be on its way out ( had to use the throttle a bit to keep it running for a few seconds after it started this morning) I havent got time to take it to a dealer for at least 5 weeks, so I just ordered a new MAF at a good price to see if that helps. I could always sell it again if it doesnt.
You mentioned the o2 sensor, where is that located and what would the replacement cost be? ( Haynes manual hasnt come yet!!)

Allan

 

[jberks]

I believe the o2 sensor is in the exhaust system near the cat but the garage replaced mine so I can't be certain. Basically, I had a problem where I would accellerate, the car would pick up and then a few secs later I would get another lump of accelleration, rather like pressing the throttle a little further. At the service I had a diagnostic done and the 02 sensor was diagnosed as being on the way out. A week later I was driving home, same thing only instead of picking up, it died and I crawled home down the motorway at 40. It was running so badly I didn't dare switch off though I've since discovered that this would probably have returned it to normal. This was my first experience of safe mode. Anyway, dropped it off and they replaced the 02 sensor and the MAS (MAF) and all was well again.
Whether I actually needed the o2 sensor I don't know, but it was already waiting for me so they'd fitted it, expecing that to resolve the problem. Only when it didn't did the pop a new MAS on it. I believe the o2 sensor was around £90.

So, I believe you've done the right thing, chances are the new MAS will sort it.

 

[bigdave]

bibamus,where did you order your maf from and how much was it
regards dave

 

[bibamus]

I got it off ebay( no idea who made it), but I am not sure it works properly. I changed it when the engine was hot,( dont know if it makes any difference) started it up and the tickover wasnt very steady. I also had delayed gearchanges, but, on the plus side, the hesitation seemed to have gone. I paid £69 for it.
I read through the forums and saw someone had cleaned theirs, so I took the old sensor out of the housing and sprayed contact cleaner on it a few times. It has definately made it better, not quite right, but almost. Hesitation has gone, gear changes are smoother and idle is up to normal, just a little too much drop in the revs when selecting gear.
I will try the new one again and give it a proper test, if it is still not right, I will send it back and maybe get a genuine Bosch one later. But for now, the car seems better.

Allan

 

[television]

To be truthful it would not be a bad idea as owners of cars that are going to need a MAF sometime to keep a spare one in stock, Deisels get through them quicker than petrol, this would only apply to cars after around 94 as different sensors were used before that, They had the reverse effect on the engine.

malcolm

 

[television]

You mentioned the o2 sensor, where is that located and what would the replacement cost be? ( Haynes manual hasnt come yet!!)

Allan

The o2 sensor is in the exhaust system, just before the cat, some cars have 2 with one after the CAT, the best time to change it is with a new CAT as it does protect it. Cheap and easy to replace

The EGR valve on the exhaust manifold when faulty only effects idle

Malcolm

 

[askey79]

hi could this be the fault with my a class as you have to put your foot thru the fllor to get it to go anywhere till it gets up to around 3000 revs. also there is a strong smell of petrol when i pull up.

 

[bigdave]

is it true that i will have to get my e.c.u cleared when i replace an air flow meter on my 1998 c180 sport
cheers

 

[television]

is it true that i will have to get my e.c.u cleared when i replace an air flow meter on my 1998 c180 sport
cheers

The car normally runs OK on just fitting the filter, this is not a part of the car that needs the codes clearing. Have this done on the next service,anyone with an HHT tester can do it, if only to leave everything clear till the next time. Faults are not always recorded for this device, but others may be thrown up.

Malcolm