1999 infiniti i30 running rough at idle (fixed)

[chalupa batman]

Hey there. I'm new to the forums and new to owning a Nissan/Infiniti. I've been browsing here and elsewhere since I bought the car a few months ago. Anyways I've occasionally seen people say they've had an issue with their car running rough at idle and thought I'd share my story in case it helps anyone.

Symptoms: car idling rough while in gear and not moving, idles rough in neutral and park but far less noticeable (watch tachometer for rpm drop, runs smooth @ or above 1500 rpm), hesitation when accelerating from stop or low speeds (under 2000 rpm runs rough, @ and over 2000 rpm runs smooth), CEL not on but occasionally throws a code then quickly goes away.

Known recent repairs from previous owner: alternator, spark plugs, battery, k&n air filter, valve cover gaskets (all parts less than 1 year old). These replacements were done by the owners husband.

Series of events as they occurred for me:

First month of driving I noticed the car ran a little rough at idle and would sometimes come close to stalling. Eventually CEL came on with a MAF code(don't remember the exact code sorry). I decided to look at the air filter, MAF, and throttle body. All were dirty and the MAF sensor had a red film on it I suspected to be from the k&n filter oil. Cleaned all of them and CEL went away, car runs smoother but still semi rough at idle.

2 months later car begins to run rougher, shows definite signs of misfiring, accelerates horribly, and eventually engine misfire code pops p0306 cylinder 6 misfire. I swap ignition coils for #6 and #4 cylinders, code changes to p0300 multiple cylinder misfire. I assume this means the #6 coil was bad and since I didn't drive it more than a few miles the code didn't change from p0300.

I decide to change out all the coils as part of maintenance since they looked original, or old at the very least. Also changed out the fuel filter, cleaned the MAF unit (red film again), and added some fuel treatment to the gas tank to absorb any water since it's winter time.

Engine light goes away, runs way better than before, but still idles rough. I drive it for a week and the CEL pops again p0300. At this point I'm suspecting a vacuum leak.

I begin checking visible vacuum lines for any obvious tears/cracks. They appear fine. Next step I spray potential hard to spot areas with starter fluid. When I spray around the idle air control rpm drops drastically. Next step I take a cigar and blow heavy smoke into the big vacuum line that goes into the idle air control from the MAF housing unit (forgot the specific name for it). A noticeable amount of smoke comes from the back of engine (near firewall and IAC) as well as underneath the throttle body. I look at the back of the engine and see a bolt from egr to intake completely loose. I tighten it and repeat the previous steps. No smoke from there and engine no longer drops rpm when I spray fluid near IAC.

Stills runs rough though and I suspect it's coming from the rest of the EGR assembly underneath the throttle body. I don't have the tools to find the leak or remove the things needed to get there so I take the car to a technician.

He does various test and can't seem to find anything other than a bad coil. He checked it with a new one says the car now runs fine. I tell him I just replaced them and that I'll swap it as it's under warranty. I offer to pay him $200 for his time but ask him not to swap the coil. When I pick the car up he hands me the coil he said was bad and ended up replacing it anyways.

No more rough idle! I'm of the belief the coil was just fine. That the tech found something that was loose and tightened it just like I had mentioned before. As a way to justify charging me for something he replaced the coil when asked not to. They did test the egr valve for proper function and said it was fine though

I believe that when the valve cover gaskets were replaced a few things were left loose. Hard to reach bolts and vacuum lines.

I realize there wasn't a definitive answer here but the situation is very telling. Hopefully someone can use this to help solve a similar problem if it ever comes up.

I'll update if anything new comes up. Any questions feel free to ask

[Q451990]

to NICO!

That's a great first post! And any diagnostic procedure that involves firing up a cigar to smoke the intake is pretty cool...

Heath

[95maxrider]

I'll second that! That's a great at-home vacuum leak detection method, I might have to try that! There's a good chance you will need to clean out your EGR and IACV at some point, but until then, happy driving!