Unwanted engine braking.....

[seismic22]

E36 323i

Coming off the throttle and the car seems to have excessive engine braking down to very low rpm and then it suddenly seems to back off again. The car always feels like this but it is sporadic in its severity. This is my second E36, in fact I ran this one against my old one for a while and there is definitely something up. Cars had new front calipers and backs dont seem to be dragging anything unusually.

Note: The car does seem to be a bit more/less punchy sometimes but generally if you nail the throttle it goes pretty well and it always feels pretty torquey. Car occasionally has very minor hesitation upon stabbing the throttle at low revs.

Im thinking air leak of some sort but it seems a bit of any odd symptom to me, can the wisdom of Pistonheads offer any advice?

Thanks!

[the stigs dad]

How long has it been since a full service? Get the car on a ramp or axle stands and check all 4 wheels move freely.

[SMGB]

If you put it into neutral and let it coast does it still stop the same, if so binding somewhere. first candidate is the brakes.

[seismic22]

Coasts in neutral fine, will roll back/forward if left on a slight slope without the handbrake on.

Front calipers changed, had whole car up on axle stands and all 4 wheels ok.

Cheers.

[the stigs dad]

I'd change the gearbox and engine oil.

[Astra Dan]

That sounds like the overrun cut off operating. Generally the engine will be re-fuelled about 1500RPM.

Does it seem to jerk excessively if you reapply then let off throttle again?

[Fort Jefferson]

seismic22 said:

Note: The car does seem to be a bit more/less punchy sometimes but generally if you nail the throttle it goes pretty well and it always feels pretty torquey. Car occasionally has very minor hesitation upon stabbing the throttle at low revs.

Badly worn cam shaft, so the exhaust valves are not opening properly, or a blocked exhaust?

This would explain why it still feels torquey but less punchy, and excesive engine braking.

[Crafty_]

Seen this before on slightly older cars that have a cable throttle.

The cars in question had a air idle valve, this was the throttle bypass that allowed the engine to idle when throttle was closed. the valve has a disc in it that rotates, part of the disc has a hole in to let air through.

Expected operation is that at idle the disc rotates to where the hole is, air passes through and on to inlet. When throttle is applied the disc rotates to block it off and prevent air going through it, thus all air goes through the throttle body.
When the throttle is released the disc opens slowly as revs drop, so by the time the revs reach idle the disc rotated to where the hole is and air can pass through.

When the valves get old and gunked up they don't open smoothly, then suddenly fly open.. so when revs are dropping the engine is actually (mostly) starved of air and is being pushed by the drivetrain - lots of what feels like engine braking. Suddenly the air idle valve flies open and the effect of the engine braking is reduced.

Have no idea if it applies to the engine in question, the post just reminded me of it.

[Kitchski]

Throttle positioning sensor.

[seismic22]

The car has excellent service history, 116k and has recently had an oil change.

I dont see any reason for a worn camshaft but I wont discount it.

Blocked exhaust is a maybe but shes running a 328i cat back exhaust that aren't prone to failing. My last 323i had a blocked exhaust, the normal 323i system is prone to blocking and the car lost all power below 4k when that happened.

Ill look into the air idle valve.

TPS sensor is a good shout - it was smacking the underside of the bonnet until recently when i changed an engine mount and it was throwing a code. Its now no longer lighting the warning light on the dash but thats not to say its not fubared.

NOTE: Today I realised it seems the "excessive engine braking" like symptom seems nearly non existent when cold and alot worse when shes up to temp. I think anyway............

Thanks for all the suggestions, ill take them all into account but any further opinions are welcome....

Cheers!

[seismic22]

Anybody?

Currently looking into the air idle valve,, going to try and get a friend to get codes read and try and get a second hand throttle position sensor from the breakers tomorrow. Also looking for a second hand cat/exhaust center section to rule that out (i can scrap the old one for the price ill pick up a second hand one!).

I was wrong symptoms are still there even when cold. Engine performance in general has dropped.

[davepoth]

Idle control valve sounds like a winner to me. Likely to be full of oily gunk.

[Huff]

Idle air valve is a very good call. I had very similar symptoms to this on a Saab, which could drive like a very jerky thing. Pulling the (universal, Bosch) IAV part and giving it a good wipe-out with solvent, followed by a generous oiling to the moving part (NB never, ever force it to move) made a world of difference. Usually easy and quick to check - a jubilee clip or two at most.

Otherwise I'd also check any vacuum lines for cracks and splits, the kind of thing that might open up with movement; especially the one usually connected to the fuel pressure regulator (generically - I don't 'know' the E36). The fact it goes fine when the throttle is well open (ie low/no manifold vacuum) might be a hint.

Oh, and on that point is there any kind of oil breather recirc valve into the inlet manifold? If these stick open too long you can get odd /unpredictable driveability issues.

[HustleRussell]

Kitchski said:

Throttle positioning sensor.

I was thinking this, or it's corresponding actuator on the throttle body assuming it's drive by wire.

[seismic22]

UPDATE:

Changed the Throttle position sensor for a second hand item I grabbed down the local scrappy and hey presto the car drives better than ever!

Thanks everyone who contributed to this thread.