M20 Stutter When Gas Pedal Sharply Pressed

[sierra9260 4]

Hi all!

Over the summer I had the opportunity to do a huge overhaul on my e30 320i and I must say I have completely revived the tired old girl. I have put a nice new engine in, removed some rust, changed the transmission from auto to manual and shes running very nicely. A little niggle I have found is just that when I quickly or sharply, press the accelerator pedal the engine splutters a little and the revs drop for a moment, kind of stutters and then will sort itself out. I will try and pop up a video shortly.

Before I changed engines the car had a myriad of problems and if memory serves me right, this was one of them. However it is a massively watered down version of the problem and it doesn't really affect the general runnings of the car to get from A to B. The only things that weren't changed when the engine was swapped was the fuel pump and MAF sensor. Basically everything else has been changed over.... On a side note a fella was trying to help me sort some idling issues on the old engine and started playing with the MAF sensors allen key adjustment screw.

one other little niggle I have is the engine revving past 2k revs when it is first started for the day. I'm assuming this might be as simple as changing the thermostat? I have put in a new radiator too and I thought the car might just sort itself out when the water has cycled etc etc. Any input here, as always is greatly appreciated. This car would probably still be a giant paper weight if it wasn't for the really good people on these forums so many thanks!

Edited February 7, 2014 by sierra9260

[Kepes 231]

Since the fuep pump wasn't replaced while you were doing the overhaul and from what you describe its possibly a bad fuel pump. Another symptom would be a bad idle that would climb then drop etc etc. If it's prefacelift you'll have a transfer pump in the tank and an external fuel pump. Otherwise it'll be just one in the tank. Theres a way you can test to see if the fuel pumps are working fine in the bentley manual but I can't remember exactly. Sorry if thats all a bit of a ramble, im just kinda bored waiting for my brother to get his hair cut :-)

Edited February 7, 2014 by Kepes

[_ethrty-Andy_ 2122]

where abouts are you? if your in wellington im sure i have a spare M20 AFM here we could try.

but it sounds to me like its probably the throttle position sensor, with both the 2k problem and the stutter could be cuased by, where as the AFM could cuase the stutter too, but unlikely to make the car hold its RPM at 2k in the morning.

[sierra9260 4]

Good points there chaps, changed the fuel pump with a wreckers one when the old engine was in the car and didn't seem to make a difference, although there is a possibility that pump could have been bad too.. The idle is very steady though and doesn't play about at all. My pump does have an audible buzz but I was under the impression this isn't anything too troublesome?

I am usually wellington based Andy and that is a most kind offer but the car is in Hawkes Bay where its currently being worked on. Although I appreciate the offer. Another interesting point I have just thought of is that when revving high on cold start if left for a while then turned off, then back on the idle drops... Almost as though you have reset something by turning the key. I will try another TPS then I'm afraid I'm all out of ideas but I'll see how this goes.

[_ethrty-Andy_ 2122]

Good points there chaps, changed the fuel pump with a wreckers one when the old engine was in the car and didn't seem to make a difference, although there is a possibility that pump could have been bad too.. The idle is very steady though and doesn't play about at all. My pump does have an audible buzz but I was under the impression this isn't anything too troublesome?

I am usually wellington based Andy and that is a most kind offer but the car is in Hawkes Bay where its currently being worked on. Although I appreciate the offer. Another interesting point I have just thought of is that when revving high on cold start if left for a while then turned off, then back on the idle drops... Almost as though you have reset something by turning the key. I will try another TPS then I'm afraid I'm all out of ideas but I'll see how this goes.

TPS isnt too bad to change, but not as easy as the AFM. Try that first if you can get your hands on one. Id like to say id ship you one, but an AFM can be quite sensitive especially at this age so rather not ship it.

Idle control valve is another posibility for the 2k issue, but not the stumbling on jabbing the accellerator.

I cant rememeber if the M20 can do that diagnostic stuff, if it can the DME/ECU should be able to tell you what the issue is if you have some way to scan it

[sierra9260 4]

Looked up some videos on youtube of faulty air flow meters and a little trick some people use is disconnecting the plug while the car is running. If the engine starts running more consistently or 'better' when the plug to the sensor is disconnected chances are you're in the right place. I did this to my air flow meter and the revs dropped and it seemed to just idle there, a lot better than it does with it connected.

So now I'm really after an Air Flow Meter.

[_ethrty-Andy_ 2122]

well there is one here for you. Id rather not risk shipping it, but as it turns out, should be heading there within a few weeks to pick up a new toy so could bring it up

[sierra9260 4]

well there is one here for you. Id rather not risk shipping it, but as it turns out, should be heading there within a few weeks to pick up a new toy so could bring it up

Thats awesome Andy, thank you. Do you know if it will be compatible with my engine and things? The engine is 1990 so im fairly sure it would have the updated motronic system with the o2 sensor etc, I think the maf plug has 4 pins + a dud pin so its like a 5 pin plug. Fair call on the shipping side, ive seen a few on trade me but if you're coming up I'll just wait. Thanks mate, fingers crossed that will sort it out

[antil33t 90]

I had an issue like this with my M20B25, and I could never, ever figure it out.

[Driftit 1952]

I have had this problem a few times in my E30 Series car. The TPS fills with oil and causes a stutter when you hit the gas.

Quite noticeable in the race car where you need full throttle 99% of the time.

With the engine off and the throttle 100% closed you should here a little click when you start to slowly open the throttle by hand.

Should be a sharp little click. If it is dull or not there at all you may find its got oil in it.

The TPS is on the bottom of your Throttle body. The oil runs down the main shaft on the M20 and straight into it.