TPS causing misfire?
 

Checking the TPS, checked out ok, thought I'd set idle speed while i was there as it's pretty low (500rpm approx), idle speed didn't adjust.

Am I doing something stupid?? or do I need a new TPS and could this be causing the misfire I've been chasing around for ages?

Got the same problem when it starts I replaced the TPS and it's not solved the problem, if you have any luck sorting it let me know as I'll be interested.

I'd be checking to see if the air intake and intercooler piping is leak free.

Any unmetered air will cause it to idle shit.

Oh and it unlikely to be the TPS. If this is buggered the engine will idle faster, unplug it, you'll see.

when does the misfire occur?

Only had chance for a quick fiddle this weekend, but I did find a new dizzy cap on the shelf in the garage which I thought I'd fitted :trout
. . . fitting this improved things quite alot, but there is still a slight misfire (sub 2250rpm).

Unplugging the TPS has no effect what so ever, which drew me to the conclusion it was buggered.

I had a look for air leaks, as I blocked off the EGR (?) pop off valve, but found no traces of oil mist leakage, the only place i did find some is by the turbo outlet, but it's hard to tell if it's new or not as the rubber seal was ripped when I first got the car.

You can deffinately hear it coming on boost, but it's not no sound deadening under the bonnet and a cone filter now.

I've brought it into work today, so I will go home the long way and see what it's like now.

I would check the TPS switch is closing at idle, it might need adjusting. You can check it with a multimeter.

Still can't see this causing a missfire higher up in the RPM.

Right, had to take the boss home as he's ill, so got another chance to see if the misfire is still there and it is.

Sub 2.5K rpm and only on light throttle.

Slightly heavier acceleration, it sometimes hesitates very slightly then revs cleanly.

Does it whether engine is cold or up to temperature.



It's had new plugs, HT leads (8.5mm magnecor), dizzy cap and fuel filter.

Drives lovely on the open country road, but is annoying to drive through town, still induces big grins, specially as it raining :D

if its low rpm maybe an inlet manifold air leak? usually when the turbos boosting sufficiently it masks small leaks. try having the engine idle and spray wd40 around the manifold, if the revs rise its an air leak in the vacinity of the WD40 spray.
maybe split in hose from AFM to turbo, again maybe slight so that its being masked when boosting?

I shall give that a try! :)

It's definatley an air leak!

Tried the WD40 trick, but struggled to hear the rise in rpm, did notice it running slightly smoother though, took it for a trip down the shops and it drove lovely, on the way back it start misfiring again, so I know what it is just need go back and do another WD40 check.

Not sorted yet but not far off.

Good call chaps! :D

See that why I'm a pro ;)

if all else fails - try cleaning your hotwire in the MAF

Did this ever get solved as i have a similar problem.

Although mines okay when cold it does it when up to temp.

Be good to know if this got sorted and how as i have the exact same problem as Irmdave. Missfire at idle and on light throttle upto about 2500 rpm.

Have change plugs, leads, rotor arm, dizzy cap, coolant temp sensor and still no luck.

Was thinking dropping resistor as have heard about similar problems with these on the s13 but not sure if the s12 has one?

Any help would be much appreciated :confused:

Air leak was the problem.