Engine behaviour

x-driver

x-driver

Active member
 Slovenia
Lately I've noticed that when the car is still warming up and I'm driving normally, when I accelerate and switch gears up, in the moment when I release the clutch pedal in press the throttle, instead of accelerating further on, the car acts like if something would suffocate the engine for a split of a second, then it continues to accelerate. It only happens every now and then, not always.
The car also feels like it lacks power. Not a lot but noticeable.

Another thing that I'm noticing for a long time now with the engine is this. At cold start, when I switch in reverse and start to move, when I apply a tiny amount of throttle to move the car from stationary, the revs begin to jump up and down very quickly for about 100-200 rpm. It goes away instantly if I press the throttle more or if I step off it. Happens only once per cold start.
There were no codes last time when the car was checked.

Any idea?
 
How many miles on your Z?

Sometimes the MAF sensor can give your car's computer incorrect values due to age and it being possibly coated in a layer of dust/dirt etc. You can remedy this by buying a MAF cleaner spray and spraying it on the MAF sensor and cleaning it thoroughly then re-installing. Cheap enough to give it a shot.

It could also be a slight vacuum leak giving you that stumble and slight lack of power. Check the intake tubes for any splits or cracks or if anyting is loose. A slight vacuum leak can do that to your engine without triggering a code -- if it gets bad enough it'll throw a code but you can easily find out by trouble shooting.

Another thing is the DISA valve since it's responsible for the airflow at lower RPMs which gives you that low end torque. That could be soft failing too.

It doesn't sound like anything alarming at all, so check those three things first without going to the more obvious and expensive ones (fuel & spark)
 
Agree with above. I'd also put some fuel system cleaner, like Techron, in during your next fill up. I had occasional choppy cold starts and putting some of that through cleared it up. Probably not your issue, but worth doing anyways.
 
Most of what @Motionblurrr mentioned has already been done in last 2 years. The car has currently 136k km (84.500 miles?). The intake boot was replaced 2 years ago. The MAF was cleaned last year and actually made some difference (which is gone by now). DISA has been rebuilt with one of those british kits.

In this time also the CCV was replaced, also spark plugs and one coil that failed, the valve cover and intake manifold gasket.

The car was more or less stationary for some years before I bought it, so there were plenty things needed to be replaced.

Anyway, what else could be causing troubles here? Vanos? Maybe MAF again? Or is it too unlikely?

Oh, one more thing. I also noticed just recently a bit worse smell out of exhaust when the engine is running cold, than it used to be. At least I think so. It's also true that I recently started to step out of the car and go behind it to close the garage door when leaving. Where it was parked before I would reverse the car out of the garage and go close the door in front of the car. Less smell there I suppose.
 
Sounds a wee bit similar to a slight rev hesitation I get every once in a while and am still trying to identify it.
Have you tried a smoke test on the car to check again for any leaks? Also, maybe connect up an OBD scanner and look at some live data to see if anything looks strange on a particular cylinder. I am going through all of this now, without any joy. My next step is to pull the injectors out and test them incase they are dirty.
 
Smoke test was tried last year but maybe it's time to do it again. I also didn't manage to get to the OBD scanner yet (since the last issues appeared). So no news from me yet.
 
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