1990 318i has developed a cough

[parakeats]

So, after a few other issues had been seen too, it's now developed a really annoying cough! It's like one missfire at around 1000-1200rpm when accelerating in a higher gear. Just drove to Bristol from Plymouth and it didn't had a problem at all and performed right the way through the rev range, but now it's got a cough which jerks me forward and back when you're at low revs accelerating.

Just refitted the rocker cover, it's used all the water in my radiator again, but doesn't show any sign of overheating, leaks or dropped performance. when it has this cough, the mpg meter seems to shoot up past the 50 mark if that info helps? What are the bits I should be checking tomorrow? Sorry if this could have been found with a search, I'm on my phone and it's making it slightly harder to do so.

[BHadley]

Is there any "mayonnaise" style gunk on the oil cap or dipstick ?

What was the inside of the rocker cover like any gunk there?

Does water run out of the exhaust tailpipe of is there any steam?

Any puddles under the car?

Aside from that look at the 318is info on the wiki on this site....

[parakeats]

There was mayonnaise type stuff under there and on the underside of the rocker, but i cleaned it and it's not come back, and my water never goes down more than 0.5l maximum which we've put down to a possibly faulty cap? And no water under the car and doesn't steam when hot. Oil is really clean.

sorry the pictures are huge. Before cleaning the rocker


And the cams at the same time


I had a fiddle with the ht leads and plugs earlier and it seemed to not do it as much, but it still does it a couple of times a trip of about 5 miles or so, thinking about investigating plugs and leads more, possibly replace as they didn't get done last service, only oil and filters. Maybe run an injector cleaner (dad said it felt like a spot of bad fuel could be the cause) so might out some in for luck unless it's advised against on these?

[Brianmoooore]

when it has this cough, the mpg meter seems to shoot up past the 50 mark if that info helps?

This would indicate loss of the fuel rate signal from the engine ECU to the instrument cluster, which is derived from the signal to the injectors.
Any corresponding drop in the rev. counter needle?

[parakeats]

Yeah the rpm needle drops, sometimes does it while idling and almost stalls

just done 120 miles back down the motorway to Plymouth and it didn't miss a beat, ran well all through the rev range and sat nicely at 80... I dislike intermittent faults!