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Idle surge problem and misfiring

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98gst14b

15+ Year Contributor
453
0
Jan 24, 2006
Keys, Florida
Wether the engine is hot or cold itll just bounce up n down forever, and at about 3500 rps it sounds like its missfireing, dtc's show barometric pressure but I dont see a map sensor anywhere, I dont think my car has an egr valve maybe it could be the iac? Where is it located? Anything else I should check? Thanks
 
I tested the isc and everything turned out good, could this problem be ecu related? How can I check the condition of the ecu should I replace it?
 
One more thing, I just noticed that there is some silicone sealant in where the biss screw goes, is this bad? Should a little air be getting down in there?
 
No their isn't supposed to be any air going down their. Looks like a bandage fix for some bigger problem. Take the silicon out and the BISS screw out and check the o-ring. Take the throttle body apart and clean it, make sure all the gaskets are good. Check for boost leaks.

Also, check your ignition components, injectors, capacitors, plug wires, plugs, coil packs.
 
Do boost leak test too as it will tell u if your biss screw is leaking and show you any other leaks that could potentially mess with the idle.
 
Boost leak test came out good, I have 22 inches of vacuum at idle too. There might not even be a biss in there I'll just order a new one with o-ring and replace it. As for now should I visually inspect the ecu? Also how would a bad idle switch effect my idle? If I unplug it itll stop surging but the idle will go way up. Thanks for your replies.
 
IF you want to visually inspect you ecu, when you take it apart look for abnormal signs like black like a short; but i highly doubt its your ecu. Yes, a bad idle switch might be a culprit, try testing your TPS to see if it adjusted correctly. Check your timing. Check your coolant temp sensor.
 
My logger shows 12.5% at idle tps. Timing jumps all around cant really tell what it settles at around 15 degrees or somthin, but I tried adjusting the cas and it didnt seem to change the timing on the logger much. I dont think the coolant temp sensor is bad because my wideband is reading 14.7 at idle, but where is it? In the t-stat housing?? And how can I test the idle switch, at dead idle the switch puts out like 60 ohms is this correct?
 
OK UPDATE: I decided to remove my TB and clean it. I cleaded it, and tested the ISC and it works perfectly, I followed all of the surge troubleshooting tips and I still have surge! I messed with the biss screw and nothing. I set my tps to 0% and nothing. Wats happeneing!!!
 
Its hard to set the biss when the car is surging, when I unplug the isc the car still surges, I tried screwing all the way in and out etc and it didnt change anything. I think the coolant temp sender is good because my a/f's are perfect.
 
Remove the isc from the tb leaving it plugged and have somebody start the car while you look to see if it's moving.

If it's not moving, you can open the isc up via those 3 phillips head screws and manually extend the valve out all the way and reinstall it. The car should no longer surge if it is indeed a bad isc that is stuck and letting extra air in.

If this fixes the surge, than either your isc is bad or your wiring is ####ed somewhere no longer allowing the ecu to move the isc to control the idle.


Hope this helps
 
The ecu looks brand new, everything is good i cleaned and reinstalled the tb, but I found these two sensors on the thermostat housing that I missed before, could they be causing the idle surge? What are they? Heres a pic of them:

http://i114.photobucket.com/albums/n279/98gst14b/100_0500.jpg

Also I looked at the biss screw again and noticed that it had a small crack on it, is there anywhere I can get a biss screw overnighted to me? Because at this time of year itll take two weeks to get here. THanks
 
Biss screw can be gotten from www.jnztuning.com (order by phone) along with a new o ring.

Those sensors are coolant temp sensors for the ecu and the dash etc. I doubt they can cause idle surge but you should clean them regardless :)


PS: if your biss screw was cracked, it would have leaked during the boost leak test.
 
Ill ohm test those coolant sensors, the biss screw had clear silicone over it i guess to keep it from backing out/leaking. It will probly leak now but before silicone kept it from doing so. BTW I think my ecu is a socketed eprom b/c one of the chips said :550 cc No Fuel Cut Rev Limiter. Ill reinstall a new biss, and boost leak test again.
 
OK, I sealed off the biss screw hole temporarily and boost leak tested. The test was perfect it went up to 20 psi and sat there. What do I do next?? Iv investigated every possible scenario. Does my car have a barometric pressure sensor? Because the dtc's are showing me that.
 
If you have a DTC for the baro sensor you'll need a replacement MAS since they're integrated.

You can usually find parts like this at a local pick-n-pull or Mitsubishi Graveyard.
 
Is the stock boost gauge reading from the mas? Because sometimes with the key on it reads -7 some times it reads +7, and sometimes it dosent work at all.
 
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