First off: merry Christmas to everyone on the forums!
Now for the issue: I have a 1997 2.4l sunfire 5 speed.
It is misfiring at low throttle such as under around 50%. I have checked and it has fuel pressure and the whole fuel system is working properly. It is getting spark and I tested compression and all cylinders read at least 210+. When in neutral the car has full range of power with no misfire even at low throttle. When I'm driving the car has full power at wot with no miss. Just when I'm cruising a low throttle it acts up. It's definitely not rpm dependent. I just replaced the computer and it's been running fine for the week it's been installed. I've searched and can't find anything like it. Also changed all sensors on the throttle body and still no change in performance. Any help would be nice!

if you know how to use an ociliscope check your map sensor and tps my car had a part throttle miss/buck especially noticeable uphill it turned out to be a bad throttle position sensor i fixed it on accident when i put the 2.3 throttle body on my car

Well revisiting this issue.
It only misses while I am decelerating in gear with no throttle and in neutral the rpms fluctuate between 800-1200 and sometimes goes clear down to 500 nearly killing the car. It's drive able just annoying as hell! Anything common I should check? Tried changing the map, iacv, and cam position sensor with no results :/ it's getting annoying cause I wanna enjoy my cavfire without putting more money into it

so the new ECU eliminates the problem? you may just need to have your stock ECU tune looked at...like one of the fuel perameters may be messed up at a certain RPM range or something..Cant you just keep the ECU in that you replaced it with? Or am I reading that wrong?

Also, have you checked for vacuum leaks while the engine is running? It could be a very small leak somewhere. 800 to 1200 is a huge jump as idle with it warmed up. Do you have any mods? Have you changed your plugs, air filter, oil, etc (basic tune up)?


04 Cav. 2dr. 5spd. My DD. 'Nuff said.

Mods are just a walboro fuel pump. Spark plugs changed last night, cylinder 1 & 2 were soot covered and the other two were great. Maybe injectors leaking?

Here is a scenario of my driving experience today while delivering pizzas:
Take off and it accelerates fine.
Get to the light and idle fluctuates between 500 and 800 and the car almost dies with each fluctuation.
Take off and go through first second and third, let it rev down in third and when it gets to 1500 it jerks and sputters.
Put the clutch in for the light and the car dies, pop start in second to regain life.
Idles fluctuating again at this point.
Any ideas based on that?
New map sensor, tps and iac with no help. No vacuum leaks tested with carb and choke cleaner. Out of ideas at this point. Searching has yielded no results I just want my car back so I can enjoy it, at least I still have my WOT for the fun stuff

when did you install the upgraded fuel pump? I had issues after installing my Racetronix to where I had to drop the tank 3 times to get it right. The small venturi valve if i recall was the culprit. i did not have the clamp tightened down as tight as I could get it and it was leaking back into the tank (all internal). That fixed my idle issues after the pump installation.

But again...what about the ECU? Have you verified FULLY all vacuum leaks? if the injectors were leaking you'd know it. You'd smell it and there would be fuel/dirt all over the injector, injector plenum/port, and on top of your manifold. also verify your fuel pressure regulator is not leaking, though that leaking I dont think causes misfires its just a noticable leak.


04 Cav. 2dr. 5spd. My DD. 'Nuff said.

The car was in an accident where a guard rail had hit the passenger front tire square in the middle and took off the ecu, emissions and goodies. Well I went through the harness on the computer and resoldered, and heat shrink wrapped all the bare wires I could find. Still hasn't fixed my issue. The ecu is from a scrap yard

Just posted this in another thread. Have you tried replacing the ignition coil housing? See if that helps. If not, your issue sounds bad enough that it could be then ignition control module. I would only replace the ignition control module after you verify all of your coils, plugs, and "wires" are good.


My 98 ls 2.4 used to have an idling problem while stopped. Ignition coil house was to blame most of the time this happened.



MaTtMan
98 Ls AuTo