Idle Surge.

[theoutlaw82]

So I have read several FAQs about this on this site and others as well as the Factory Service Manual. But I still have some questions.

When I start the car it runs smooth at 2000rms for about 2-5 seconds and then starts surging between 1500-2000rpms. My boost vacuum gauge reads 18-20hg so I guess that eliminayes vacuum leaks. CEL is not on so I replaced the ISC motor and it didn't help. Plug is missing from the BISS so I'm gonna replace the o-ring as a percaution since its cheap. Also gonna pull and clean the throttlebody and replace the gaskets on the manifold and elbow. I also plan on checking the idle switch adjustment and tps adjustment as per the factory service manual.

Now heres my questions.
1. Wouldn't the CEL come on if it was a bad senrsor?
2. Could the egr be leakin vacuum without throwing my gauge off?
3. Since it does it in both closed loop and open loop mode doesn't eliminate the o2 sensor?

 

[92AWDHX40]

Terry's Talon Troubleshooting Tips #3 - Fast Idle (aka. Idle Surge)

 

[theoutlaw82]

Terry's Talon Troubleshooting Tips #3 - Fast Idle (aka. Idle Surge)

Thanks but I already read it several times.

 

[92AWDHX40]

So what didnt you check once you read the thread, did you do a blt. I would eliminate one thing at a time, i had bad sensors and didnt show up as a cel. You may need a tested isc, vacuum leaks, throttle body may need to be rebuilt, a few things that can cause your idle issue. Do a boost leak test.

 

[theoutlaw82]

Actually I was going through the entire list and checking everything thats on that site as well as checking a few things I found elswhere. I'm not lookin for possible causes. I just need answers to my 3 questions above to help me isolate the problem.

 

[92AWDHX40]

I had sensor go bad and no cel,

egr valve issues could cause problems if it leaks

doesnt eliminate 02 sensor? again anything above can cause your idle issues

do you have any of those isseus. again there may not be a specifc issues with just those three things causing your idle issues, those three things yes maybe, but there, are more problems causing idle issues than those 3 things, sometimes trial and error will fix problems, and sometimes there isnt a one answer to it all.

 

[theoutlaw82]

I know the egr valve issues could cause it. The question was if a leaking egr valve would affect the reading on my vacuum/boost gauge. Reason I ask this is because I have good vacuum accordin to the gauge. Also I know on most fuel injection systems the ECM doesn't use the o2 sensor during the warm up cycle (open loop). If thats the case here then the o2 wouldn't be causing mt problem as it happens in both closed and open loop.

Ok so to add the list. Its surging between 1200-1500 rpms.
Vacuum gauge reads normal so no vacuum leaks.
New ICS.
Checked O2, TPS, ECT, and MAF with my multimeter and they all checked out good.
Screwed BISS all the way in and was unable to lower idle.
Cleaned TB.
I also noticed that there is a 1/4 - 1/2" thick layer of buildup in the intake manifold. This leads me to believe that my EGR is stuck open. So I'm thinking of ordering both the EGR and FIAV plates. That way I can eliminate the only 2 possible causes that are left.

 

[theoutlaw82]

Replaced BISS o-ring, performed free FIAV bypass from the FAQs and installed an egr blockoff plate. EGR was stuck open causing the problem. I also blocked off the EGR vacuum ports on the TB but left the EVAP system inplace since it is actually useful.