idle misfire (bare with me, I know its been covered)

[MyBeatGSX]

Yes I know this topic has been beaten to death, but after 1 1/2 hours of searching I can't find a direct answer for my situation or someone with the exact problem.

Only while idling (hot or cold doesn't matter) the engine has a miss or skip at random intervals, usually light and very very rarely it will be bad enough I thought it was going to stall. Its normally worse for the first few minutes after start up, either that or I don't notice it when I'm not parked quietly. It never misfires in the driving speed range or at WOT and blipping the throttle at idle will make the misfiring stop. There's no idle surge and it never drops more than 100rpm when it does miss. Sometimes it hard to tell if its actually a misfire or just a rough idle.

The plugs are brand new NGK BPR7's gapped at .028". Wires are questionable NGK's put in when the motor was swapped 3 years ago. Coils are original. Vacuum is usually between 18.5-19.5 in. hg at idle and 21-22 in hg in gear with the throttle shut. Fuel pressure is 36-37ish, fuel filter is probably original and in need of replacement (but that shouldn't effect the idle). Engine blows zero smoke even on a cold or humid day and burns no oil.

 

[DECODER22]

I'm having the same prob with one of my 92 GS X's and Ive done everything to try to figure it out accept i haven't changed the fuel filter gonna try that today see if it helps if you figure it out before me let me know, have you done a compression test??? i did one today and its about 150 155 149 140 maybe thats the prob dunno tho i already did the egr block off and removed all the lines that didn't help

 

[TotalEclipse112]

Check the coolant temp sensor, and the air intake temp sensor. If either one is screwed up then you could have a rich/lean misfire.

 

[ddavisaf]

Misfires are usually associated with poor spark or ignition systems. Replace the fuel filter for sure, then replace the plug wires. After that move on to the sensors that TotalEclipse suggested.

 

[tselling]

i am having the same thing going on too. i replaced all the wires and spark plugs and same thing is happening. how do you check those sensors?

 

[m1nd64m3]

Your air intake temp sensor is a part of the mas.

 

[TotalEclipse112]

i am having the same thing going on too. i replaced all the wires and spark plugs and same thing is happening. how do you check those sensors?

With a multi meter set on ohm's. Get a repair manual and look for excessive resistance across the sensor, if it reads high, open (OL on the meter), or infinity, its a bad sensor.

 

[MyBeatGSX]

Last night I was taking off the oil cap with the engine running to see what kinda blow by I have and part of my hand touched one of the ignition wires and I got electricuted (sp?) pretty good, definately not the full spark power but good enough to have 2 of my fingers numb for the next hour. So I'm guessing the wires are good and dead.

I know MSD wires have the lowest resistance but I don't see anyone running them or any online shops that sell them. I want to avoid the price rape at my local speed shop if possible..... If I can't find them then what wires are recommended (I don't want more NGKs).

 

[TotalEclipse112]

Last night I was taking off the oil cap with the engine running to see what kinda blow by I have

First off you are not going to see blow by simply by looking in the oil fill port, unless you have x-ray vision and can see into the cylinder. Blow by is where fuel and oil find a way around the piston rings, and fuel either goes to the pan or oil get burned in the cylinder, thats blow by. Secondly if you touched a plug wire and got zapped, there is the misfire problem right there. If you looked at it in the dark you woold probally se a nice arc from the wire to a ground, thus no spark to the plug, and vola a misfire.

 

[MyBeatGSX]

You can usually feel excessive blow by as a lots of air shooting out the oil cap. More so than the regular windage from the pistons going up and down and usually more constant rather than in pulses. But whatever, lets not get off topic. The problem should be found, I'm gona try to get new wires tonight and I'll post the results.

 

[TotalEclipse112]

Belive what you want but the cylinders are SEALED, there is no way to feel that through the oil fill cap. Anyways not to get off topic, lets see how the plug wires work out for your misfire problem.

 

[ddavisaf]

Belive what you want but the cylinders are SEALED, there is no way to feel that through the oil fill cap. Anyways not to get off topic, lets see how the plug wires work out for your misfire problem.

TotalEclipse112 is correct. However,
Excessive crankcase pressure is caused by bad rings, bad valve seals, bad pcv, and possibly a bad turbo seal.

 

[MyBeatGSX]

Interesting results. The wires made a huge difference in driveablity and throttle response, so much that the exhaust note is noticably smoother sounding. But the idle (although better) still tends to miss at random intervals, more so after a hard pull or when the engine (and outside temp) is hot.

 

[ddavisaf]

I'm dumb. The 7's are a little to much for your mods right now. Put them to 6's. That should even out your idling problem a little. BPR6ES. This isn't *needed* but I recommend it.
Also test your CTS and make sure it's good.

 

[MyBeatGSX]

I'd prefer to err (sp?) on the side of safety and just leave the 7's in. Better to have a crappy idle than detonation under boost. Especially considering the borderline a/f I'm running now and the fact that it creeps to 18psi.

Will leaving them in cause any problems? Maybe fouling with too much idling time, but a hard pull should clean them off right?

I'm gona just replace the CTS when I do the coolant flush, if its not dead now it will be soon with all those miles on it.

 

[Ybnorml]

Unless you tune for the colder plug you could easily have carbon buildup on the plugs, especially during normal driving. I just put in a set of the 6ES and I'm going to run them to see exactly what I have room for. I ran the 7Es before I redid the head and front engine parts but can't do that now, probably because I'm just a little off on tuning or I have a bad O2 or something.

 

[MyBeatGSX]

UPDATE:

Ok, replacing the CTS and plug wires seems to have smoothed out the idle and overall running of the engine. BUT, and trust me its a big but...

Just the other day it started with a horrendous (sp?) hot start idle misfire. It idles about as well as an all motor car with a 300* cam and 1300cc injectors. But it ONLY does this in one situation.... a hot start after sitting for over 15 mins. If I shut it off hot and turn it back on in 5 mins, no problem, 5 seconds, no problem, 30 mins, it barely runs. Reving it does NOT make it go away (unlike before), it will just misfire through the whole rev range. The strange thing is that all I have to do to make it go away is put it in gear and drive 30 ft and just like magic it idles perfectly for the rest of the drive. This is definately the strangest car I've ever owned or driven.

FYI, when idling correctly the vacuum is perfect (19-19.5 in. hg) so I'm thinking its not a boost leak. I don't see how the colder plugs could be causing this because then it would do it at other times as well. In fact I don't see how anything I can think of would be causing it because everything I can think of would make it idle bad in other situations, but it ONLY does it in the situation discribed above. And I also can't understand how driving the car 5 feet will fix the problem, but reving it up won't.

 

[90 GSX]

I'm bringing this topic back to life, this problem sounds exactly like one I am having right now. The car will miss at idle but it gets worse as the car runs for a longer amount of time (ie engine gets hotter). The thing I noticed and what struck me about this post, is that that the issue he just described about the hot start happens to me. I experienced deja vu reading that post... when you go to start the car, it idles around 500-600 missing and bogging, almost like it is fighting something. You drive a short distance and voila idling back up again. What could cause that?

 

[ddavisaf]

Ignition/Air/Fuel.
Check your plugs
Check your plug wires
Check your coil pack
Check your air filter
Check your fuel filter
Check your Coolant Temperature Sensor

Post back if none of this helps.

 

[mcleve10]

had the same problem on my 95 talon. . .changed out my fuel pump and fuel filter. it fixed it

 

[MyBeatGSX]

My car no longer does it. I replaced the fuel filter, centered the cam position sensor (it was almost full retarded), and replaced a grossly leaking exhaust manifold. The weather also got colder.

Its hard to say what stopped it. They all happened in a short period of time and after awhile I had just started to ignore the problem so I never really noticed exactly when it went away. But centering the cam sensor had a huge effect on smoothing out the idle and drivablity, the car also has significantly more power and gets worlds better gas mileage. But I believe the problem was gone before that and if I had to guess I think it was more related to the change in temperature.

Good luck and let me know what happens with your car.