M20B25 surging/juddering under load

[Daan]

Hi there.

Just took the E30 out for its first drive of the year and its got a new problem.

Only seems to happen between 1000rpm and 3000rpm, although worst at the lower revs. When you use any more than 1/4 throttle the engine judders/surges and will almost feel like its misfiring until you get to 3k when it smooths out.

Since it was last driven its had;
Distributor/rotor arm (plugs were new ~12 months ago)
An induction cone
Engine oil
Gearbox oil
Strong dose of Redex fuel treatment

So far I am thinking, fuel filter or AFM? Cant think what else could be at fault, I dont think its ignition related because it seems to do it worst under load, i.e when air and fuel are in higher demand.

May be worth mentioning the car has a lairy ECU chip fitted, but this has been on the car for a few years now.


Any help much appreciated, thanks!

[Daan]

Worth mentioning for anybody else with similar symptoms in the future, the car seems much better now after I removed the MAF sensor and bent the track arm slightly, removed and cleaned all spark plugs (New last year, but I have a slight valve stem seal issue, so the were all a bit scummy) and replaced the fuel filter, which was new around 2 years ago. Not sure which one solved the problem but they are all easy and cheap to do so worth a try.

Thanks, Dan.

[Brianmoooore]

A non functioning AFM (not MAF on an E30) would give the symptoms you describe, but I'd strongly recommend that anyone who suspects theirs may be faulty tests it first with a battery and meter, and only opens it up if it is proven faulty.