The Usual M20 Idle Blip Air leak ????

[Alex]

Like all m20's ive owned when you blip the throttle the cars revs drop and come back. If you slowly press the pedal it revs perfectly.

Ive had this problem with alot of m20s and ive never mananged to fix it. never seem to have a problem with 4 pots :S

So far with this 2 door ive fitted new rocker gasket, cleaned out the icv and tried another, drilled the tps and filled it with carb cleaner, removed throttle body and cleaned with new water pipe gasket, and throttle body to inlet manifold gasket. Ive also set the tps up so it clicks as soon as the throttle is applied. new rocker cover gasket, inspected all the rubber hoses and all looks fine. ive cleaned all the crap out of the rocker cover breather pipe too.

Any other suggestions ? its really annoying.

Can you get internal air leaks ???

When you remove the oil cap there is a slight change in running which i havent had on other m20s with the same problem so i would assume its not as bad.

Also are m40 injectors the same as m20 ones ? and can failed injector o rings cause air to be sucked in ??? and is this a common fault.

The previous owner raised the rev limit to counteract it but i want it right

[Grrrmachine]

The idle response issue isn't something you can fix; there'll always be that lag. Call it a quirk.

As for the injectors; not all M20 ones are the same. 320i are different to 325i, and one of them is compatible with a four pot but I can't remember if it's the M40 or M42.

[Alex]

They're is definitely the air leak, it splutters and coughs when you blip the throttle nearly stalls sometimes

[Brianmoooore]

The previous owner raised the rev limit to counteract it but i want it right

Unless he rewrote the ECU's software, he can't have done this. More likely he's wound down the throttle butterfly stop, which will have messed everything up! The first thing that needs to be done is to get this back close to where it was, then set up and check the operation of the throttle position switch.
The problem that you now have is that you have multiple faults - one's that may have occurred because of mechanical failure, one that has been deliberately introduced, and a good possiblity of other things misadjusted to counteract the side effects of the throttle misadjustment.

[Alex]

The previous owner raised the rev limit to counteract it but i want it right

Unless he rewrote the ECU's software, he can't have done this. More likely he's wound down the throttle butterfly stop, which will have messed everything up! The first thing that needs to be done is to get this back close to where it was, then set up and check the operation of the throttle position switch.
The problem that you now have is that you have multiple faults - one's that may have occurred because of mechanical failure, one that has been deliberately introduced, and a good possiblity of other things misadjusted to counteract the side effects of the throttle misadjustment.

Dont think anyone would do that, its been done using the screw for the butterfly stop

Ive set it up as how i think its suppose to be???????

I wound it back till its at 800rpm when warm and so as soon as a tiny but of throttle is applied the tps clicks

is this correct ?

[Brianmoooore]

To set it up properly needs special BMW equipment - I believe it's basically a pre-set idle control valve which you fit in place of the one in the car, then adjust the stop for a certain RPM.
The way I use is to remove the ICV, block up the hoses on both sides (or replace the ICV with the inlet side blocked), then back the screw off until the engine is idling very lumpily, almost stalling and threatening to rip the engine mounts off.
Once this is done, the TPS must be adjusted so that it switches immediately after the butterfly comes off of its stop.

[mcbonio]

I had this same issue on my m20b25 cab, I think its due to lag in the way the ECU processes data, quickly, but not quite quick enough in adjusting from idle to running data from various old motronic sensors.

Would a AFM to MAF conversion help? Maybe Brianmoore knows?

[Alex]

To set it up properly needs special BMW equipment - I believe it's basically a pre-set idle control valve which you fit in place of the one in the car, then adjust the stop for a certain RPM.
The way I use is to remove the ICV, block up the hoses on both sides (or replace the ICV with the inlet side blocked), then back the screw off until the engine is idling very lumpily, almost stalling and threatening to rip the engine mounts off.
Once this is done, the TPS must be adjusted so that it switches immediately after the butterfly comes off of its stop.

Will Give that a bash first of all

[fixedwheelnut]

To set it up properly needs special BMW equipment - I believe it's basically a pre-set idle control valve which you fit in place of the one in the car, then adjust the stop for a certain RPM.
The way I use is to remove the ICV, block up the hoses on both sides (or replace the ICV with the inlet side blocked), then back the screw off until the engine is idling very lumpily, almost stalling and threatening to rip the engine mounts off.
Once this is done, the TPS must be adjusted so that it switches immediately after the butterfly comes off of its stop.

The way we adjust throttle stops is back the screw off, make sure the throttle body is clean [not resting on a load of coke].

Get a piece of paper between the throttle stop screw and the stop

Screw in the screw until the paper is just pinched, feel by gently pulling the paper as you do up the screw.

Once at that point screw in the stop screw 1/2 a turn and lock it off.

That is as good a spot you will get without fancie tools