Typical causes of light throttle miss?

[JMA-RUF]

I seem to have a consistent miss at light throttle when cruising. If I increase throttle slightly, the miss seems to go away

I have all new spark plugs, dizzy cap/rotor, cleaned injectors. I also run Magnecor KV85 ignition leads.

Motor hasn't had a valve adjustment for a while though.

Any ideas anyone? Could it just be a little lean at light throttle? Should I play with the mixture screws at the back of the Motronic DME to increase the fuel mixture by 3% or 6% to see if that cures my problem?

Apart from that, the car runs very strong at WOT. It's just at light throttle cruising where it misses. Also, if I'm at idle and just raise the RPM's a little using light throttle, it'll miss, even when I let go of the throttle and let the RPM's stable back down to idle speed, it sounds a bit rough as the RPM's drop to idle.

Advice anyone?

[Rob Channell]

I have heard of symptoms like this coming from a worn AFM. There are some posts here somewhere.

[oregonmon]

I have the same problem. I guess you have to go through and see which cylinder is missing right? I'm not a mechanic and I've been talking with mine about getting this solved. I guess you can pull the wires one by one while it's running and listen to when the engine runs differently. My mechanic and I think it might be an injector that kind of dribbles at light or no throttle and than once your on the gas it sprays better which gets rid of the miss.
The worst part is driving in low gears with light throttle and is bucks, does yours do this too?

[scarceller]

Originally posted by oregonmon
I have the same problem. I guess you have to go through and see which cylinder is missing right? I'm not a mechanic and I've been talking with mine about getting this solved. I guess you can pull the wires one by one while it's running and listen to when the engine runs differently. My mechanic and I think it might be an injector that kind of dribbles at light or no throttle and than once your on the gas it sprays better which gets rid of the miss.
The worst part is driving in low gears with light throttle and is bucks, does yours do this too?

To check the cylinders one by one just pull the electrical conection to the injectors (don't pull the plug wires, they can really zap you, plus not a good idea to have them arc to ground once you pull them) pulling the injector wire does the same thing. As you pull each injector wire one at a time listen to see if the engine RPM drops about 50-100RPM for each. Also take note if unplugging one of them stops the mis fire. Good luck.

[stlrj]

I have all new spark plugs, dizzy cap/rotor, cleaned injectors. I also run Magnecor KV85 ignition leads.

Even though all these were replaced, I would still not assume that all was well with the ignition. I would spray some water on all these components while the engine was at idle to see if it makes it run even rougher.

A good ignition system should be able to withstand a bit of moisture without any noticeable change in engine vibration, rpm or sound.


Cheers,

Joe

[john walker's workshop]

pick a card, any card... could be anything. one thing that tends to feel like a real slight miss or surge is the oxygen sensor functioning. go for a drive with it disconnected to rule it out or in. carrera 3.2s also suck in the intake gaskets below the phenolic block between intake and head and that creates an air leak that lessens the function of that cylinder at idle and low rpm. unplug one injector at a time and see if each cylinder drops off like it should.