car misses at low rpms under load?

[mikeinaus]

ive had this problem for about a month now. i originally thought it was because of my o2 sensor as i was getting that code but after changing the sensor its gotten better but hasnt seemed to go away.

if im in gear around 1000rpm-2000rpm my car will randomly sputter like its not firing on all cylinders at that moment. it usually happens more when im in higher gears when a stronger load is put on the motor. im not getting any codes and im kind of confused on this one. my plugs were replaced about a year ago, and my plug wires were replaced less then 6 months ago so id say there probably in decent shape. i have no idea how old my cap and rotor are as they came with the car, but would be a minimum of a year and a half old...

gas milage is a steady 10l to 100km, no matter what i do. changing the o2 sensor improved performance but didnt really affect my milage.

im about to attempt a cross country drive and was hoping to get the car in optimum condition before i leave. im also hoping to grab a spare distributor from the wreckers just incase... does it matter what year/car i grab it from? mx6,626 or probe gt?

oh i forgot. my car has a hard time going to idle. sometimes it will hover around 1000rpm and even goes as high as 1500rpm. if i tap the gas it will sometimes drop back down to the 650rpm its set too but not always. its like the car doesnt know where the throttle is. thought it might be a problem with my iac, but i cleaned that out and it still has the problem. and solo_ryder helped me set my tps so i dont think thats it?

[Ryan]

My green car is doing this as well. I'm pretty confident its a spark issue. I'll be doing cap/rotor/plugs/wires, and I'm thinking that will fix it.

[Daninski]

Stupid suggestion but remove your neg from the battery, depress the brake pedal for 15 secs and clear the ECU memory then start from scratch. Are your plug wires good?
IPS
Connect ohmeter to 2 bottom pins (BR and BK/DB) and you should get continuity. If not, loosen 2 TPS retaining bolts and rotate until continuity has just barely been achieved. Semi tighten 2 TPS bolts.
Insert .006" (0.15mm) feeler gauge between the throttle stop screw and throttle lever. This should not break the continuity. If it does break continuity, slightly adjust TPS rotation again to regain the continuity. Insert the gauge in and out a few times to verify. (Note, it must be mentioned here that the throttle lever must be travelling the fullest extent possible to achieve a complete closure of the butterfly within the venturi. If it's believed that the idle stop screw is preventing the control arm from traveling it's maximum distance to a fully closed throttle then adjust the throttle stop screw via a 2.5mm allen key. If this was necessary, then the previous procedure will have to be started all over again).
After confirming continuity with 0.15mm feeler gauge, insert a .020" (.50mm) feeler gauge. This should just barely break continuity but completely. If not re-adjust TPS rotation again. Re-confirm by re-inserting feeler gauge.
In essence, continuity on initial connection to TPS.
Continuity with .15mm gauge inserted.
No continuity with .50mm gauge inserted.
Tighten down TPS retaining bolts.
Re-connect TPS connector.

I've done this numerous times and I still take 15-20 mins.

Cheers

[mikeinaus]

Stupid suggestion but remove your neg from the battery, depress the brake pedal for 15 secs and clear the ECU memory then start from scratch. Are your plug wires good?

i wiped the ecu about 2 weeks ago when i replaced the o2 sensor, ill give it another try but i think its something more then a simple programming error... ill replace the cap/rotor and hope that fixes the problem.

doesnt look like i have the proper tools to play with the tps at this time so ill just have to live with it for now.

[_-Night-Shade-_]

It's tricky because a lot of things can cause this. Most frequently it's just a vacuum leak. But it could be fuel and spark related as well. My MX-3 is doing a similar thing at the moment but I think it's because my timing is off.

[mikeinaus]

i just replaced the rotor and the car seems to be running alot better. its still missing randomly but its not nearly as bad as before. depending how much i can get a cap for i may or may not change it at this time. money is tight and this drive is gonna cost alot in gas...

on a side note the idle is even worse then before. im almost convinced its the tps. thinking the stronger spark is throwing it off even more. ill play around with it by hand and see if i can get it running a bit better before i take off.

[TMP39]

It's tricky because a lot of things can cause this. Most frequently it's just a vacuum leak. But it could be fuel and spark related as well. My MX-3 is doing a similar thing at the moment but I think it's because my timing is off.

timing wouldnt do that, but anyways you guys replaced your plugs wel did you check the gap before putting them in? and check your wires for dark spots, burn marks, but yea cap n rotor is alwasy a good idea, gettin corrosion on the contacts or even just worn out.

[ZeroLux]

Mine has been doing this lately too. I installed a new dist cap and rotor not too long ago, would not surprise me if those had gone bad just like the cheap a-- plug wires I bought at the same time. The plug wires already have been replaced once due to sparking out the side of the tube. I switched back to my original NGK wires after I suspected this second set (Durlasts ) had been the issue. No such luck unfortunately.

Mine usually does this AFTER it's been cold started and driven for a while but only AFTER I turn the car off and start it up warm again later. It'll run great for hours if I keep driving, and it does not do it every time, but occasionally it will act like it's misfiring somewhere. This also usually clears itself up after a bit of revving (not free revving, no sense in that) but after about 2-3 mins of standard driving in 1st and 2nd (takes a few mins to get out of my neighborhood) and wont come back until it's shut off again. It almost feels like the car needs to "pass" something, like a cylinder has some carbon in it or something is choking the ignition at first.

Anyone have any more thoughts on this? Could it possibly be an injector starting to go bad on me? I was thinking about grabbing my engine stethoscope and keeping it in the car for the next time it does this, just to see if I can hear where the problem might specifically be.

-Z

[_-Night-Shade-_]

It's tricky because a lot of things can cause this. Most frequently it's just a vacuum leak. But it could be fuel and spark related as well. My MX-3 is doing a similar thing at the moment but I think it's because my timing is off.

timing wouldnt do that, but anyways you guys replaced your plugs wel did you check the gap before putting them in? and check your wires for dark spots, burn marks, but yea cap n rotor is alwasy a good idea, gettin corrosion on the contacts or even just worn out.

Sure it would. I think my belt jumped a tooth.

[Ryan]

belt jumping makes sense too. My car runs like a bag of s--- with the same problem, and I haven't done much more than oil changes since I've owned it. It'll be going under the knife in a few weeks.

[Daninski]

My MX6 just started doing the same thing, stumbling when you press the accelerator a bit to speed up. So far I've fixed a cracked intake accordion hose and that helped but still not fixed. Sounds like new rotor and disty cap next. I always replace parts one at a time. If you change a pile of stuff and it's fixed then what part was responsible. My problem however comes and goes.

[TMP39]

well if your timing belt jumps ususally theres a a tensioner problem or jut driving it way to hard. but thats just the only thing ive seen to cause it

[ZeroLux]

Hmm... tensioner... now that's a theory I have not explored yet, and a damned good one from the sound of it. I just had my entire timing setup, belt, and water pump replaced back around March-ish. What do you think the chances are one of those components is having an issue?

The big question in my mind, is that I know jumping a tooth from the ECU's learned value will flag a CEL code, but would slack in the timing belt be enough to trigger the cam sensors to throw the code? If the bearing to the tensioner was having some trouble, it could potentially happen at random similar to what I am experiencing on my GS. I can't find any other logical explanation for the intermittent troubles, save being an ignition issue electrically or a worn injector.

I am guessing the best way to check for this is to disassemble the side of the engine again and see what's up?

Thanks for the lead, I think I'll take the car back to the place I had the timing assembly changed at and see what they can do, they have a 1-yr warranty on all work and whatever mfgr warr is on parts.

-Z

Edit: It's 1am and the brain isn't working at its best... I know the tensioner has no bearing, I was meaning more the pulley it's directly tensionING. My mistake. On the neons forums that'd be grounds for a flame-war.

[Ryan]

I just fixed my car.

I did four things at once:

- Replaced plugs (could hardly tell the old ones were V powers)
- Replaced cap and rotor (can anyone say 'buildup'?)
- plugged in my FPR
- replaced plug wire #6. It had fallen literally apart. I'll do the rest soon, I just needed to finish the job and not be late for school.

It hesistates a tiny little bit under low RPM <1k and heavy load (near WOT) but that could be from the seriously crappy wires.

The car still has a sack of issues. Constant power jerk around 4.2 and 5.4, and just generally weak, and the mileage isn't great (400-450 km/tank) VCG's have mysteriously stopped leaking oil, but it still burns coolant. I think a motor swap is in order!

[Daninski]

If your getting 400-450 klms a tank with a V6 your doing good.

So my stumbling was fixed when I repaired the cracks in my intake so no more VAC leaks.