kyddo112

Ok I bought this car (bone stock 92 SC3 5spd with K&N drop in filter) back in Sept. and it's always had this issue. It has a slight misfire at idle but doesn't affect anything else. Driving is perfectly fine and gas mileage is ok but as soon as I idle i can hear a slight pop from the exhaust and the car shake a bit. The idle seems to be random sometimes as well as sometimes it's about 700 and sometimes slightly under 500. I even raised the idle and it still manages to go below 500.

First thing I did was check the timing alignment of the cam gears and crank and that turned out in spec. Checked the cap and rotor and found the rotor loose inside the cap. Thinking that was my problem I went ahead and got a new cap and rotor kit. That didn't do anything. Changed out the spark plugs for some denso platinums gapped at .44 and that didn't do anything. Checked my coil and found out that one of the primary's weren't in spec with the resistance so I changed that, and still nothing. While changing the spark plugs I compression checked all 6 cylinders and all were 198-200psi. I also noticed none of the wires were damaged but #4 and #5 grommets were loose when I took them out. I also did the old school way and unplugged each wire one at a time to listen for any changes and all changed the sound of the motor as I undid each one.

Any ideas? I do get a large amount of smoke on cold days (more than normal I think) as the car warms up and I can def. smell fuel and my cat. converter seems a lot louder when I turn the car off. So I'm thinking it's more ignition related because of the unburnt fuel. I've checked the ignition timing with a gun and tried to adjust it with the service connector jumped and still no luck (unless I'm using the adjustable timing gun incorrectly? I set the gun to 0 and set the mark to 10 on the block right?).


EDIT: Problem solved! Previous owner had the EGR vacuum hose switched up instead of it going to the VSV causing the EGR valve to stay open during idle.

Tabaka

iTrader: (8)

The smoke at start up is either condensation or a fuel burning issue. A lot of people replace their ECU's and this fixes the problem. However, I had the same issue and replaced my ECU a while back...and it did nothing. My car still smokes like bob marley in the mornings. It's probably a slow gasket leak that gets patched up when the engine warms up or your PCV valve.

kyddo112

you think the pcv valve has anything to do with the misfire/stumble?

MrBrock

Could be the wires even if they look ok. Idle the car at night in the dark and look and listen for any arcing off the wires.

kyddo112

I wish it was that easy. I'm starting to REALLY REALLY hate the ge's intake manifold design. I hated it before but now i really really really hate it. I was thinking the same thing considering the insulation boots going into the plugs were really loose.

KahnBB6

iTrader: (5)

I'll second the hatred of the GE intake manifold crossover design. It's the same idea as the 5/6/7M intake manifolds that cross over the head.

I suspect I am having this idle issue as well but it's very subtle.

good2go

iTrader: (6)

Maybe you've got a sticking or partially plugged injector. Could also still be a marginal plug wire. Just because it runs worse without it entirely doesn't mean it can't be working, just marginally.

Also, have you cleaned your TB, IACV, and Y-pipe? They can get pretty gunked up over time. Also check the IACV stepper is withing spec and do the TPS adjustment. I saw real idling improvement after a thorough cleaning of those parts and performing those checks and adjustments.

kyddo112

do you have a link or a how-to for the IACV check and TPS adjustment? I did notice that the TB was pretty dirty. I also remember the #5 spark plug wire lead didn't have a tight fit around the spark plug so i tightened it up with some pliers to make it "snap" into the top part of the plug.

Ordering new plugs tomorrow and it probably wont get here until friday or saturday.

Maybe the k&n has dirtied the maf?

good2go

iTrader: (6)

Here's a relevant link for the IACV. It for an SC400, but it still applies.

http://www.planetsoarer.com/IAC/iac.htm

They factory service manual describes the stepper check as well as the TPS adjustment.

If you suspect the K&N has fouled the MAF, DO NOT make the mistake of using maf cleaner to try and fix it. The early MAF's are karman-vortex type which can die from the experience.

kyddo112

got new wires in today and cleaned out the tb and still the same thing. so i checked to see if the MAF might be acting up so with the car running i unplugged the MAF connector and there was literally no change in the car. didnt bog or stall or throw a CEL or anything. so i guess the MAF might be the culprit? what's supposed to happen if you unplug the MAF?

kyddo112

so during my lunch break i decided to see if i can find any codes stored in the ecu even though i haven't had a CEL come on. I jumped the connectors and got code 24, IAT. guess that confirms the bad maf as well?

kyddo112

borrowed a MAF from a friend and cleared the IAT code and still the same thing. I unplugged the TPS for a second and the engine reacted instantaneously. I tried the same thing with the IAC and got no change. Bad IAC causing misfire/stutter?