tyncobb

I have had high idle problem for the past 2-3months. And just failed Emissions Inspection for high NOx. Both NO & Dioxide at 15/25 about double readings in the 1100 and 900 range. All other emissions passed. Tech said it may be due to high idle. Bought new TPS and installed (but maybe wrong because there was almost no Spring tension....but started with electrical connection portion left of TDC because there is a rubber hose below that kept me from starting EC on th e right side of TDP as you face the engine and the adjusting TPS clockwise?). Not sure if there needs to be more tension if you remove hose and start right side turning to the left for adjustment of idle?

Also adjusted the shift cable under the TRAC cover several months ago. Could that or the cable next to it adjust the idle down.

In park at idle it sits at 2000 and needle fluctuates back and forth between 1800 to 2200 constantly about every second but the idle of the engine stays or sounds constant (not fluctuating with the needle). When I shift into Drive the rpm goes to 2000 steady and as I accelerate, the needle goes to 4000 almost, under load until I get to about 30 mph and the goes down to around 2000-2300 and then if I try to accelerate the needle immediately goes to around 4000 (but the engine does not rev with the increased rpm and as the car gets up to speed, say 60 mph, then the needle and rpms settle back down to 2000!fairly constant, unless I goose it a bit and the needle jumps to 4000-4300 immediately and I've only increased speed 2-4mph and when I let off the gas the needle drops to about 2200 fairly steady at 60 -65 mph???

I just tried finding a visible vacuum leak by spraying carburetor cleaner on EGR and IACV and hoses connections and visible pipes on top of engine and no noticeable change in RPMs.

Finally maybe this has something to do with high idle, it sounds like I may have a cracked EGR pipe but I didn't think that would affect the RPM needle movement so much but don't know what it would do to emmissions NOx??!

Any help or suggestions would be greatly appreciated. I need to pass my emmissions to get new tags which just expired 5 days ago.

Thanks to all.

dicer

Maybe get rid of the abbreviations for now TDC stands for Top Dead Center so I don't think that is what your talking about, I really didn't understand the post. Hose and starting EC ???????????
TDP Top duplicate part ... TPS we all know.

I would first clean and make sure egr is free to move.

tyncobb

Thank you for the advice to clean the EGR and make sure it moves. I will try this. As for the abbreviations, my apologies for the confusion, I'm not a mechanic and was just trying to explain all problems and probably used incorrect terms. What I meant to say about the TDC comment was that the throttle position sensor is generally shaped like a T and the top part is the spring loaded part that you screw onto it's fitting and the bottom post of the T has a female electric connector (hence the incorrect "EC" abbreviation and as the LEXLS tutorial explained how to put this piece on, was to start the bottom part of the T off to the right as you are facing the firewall of the car and then you can adjust this and the idle by turning the bottom part from right to left (clockwise). The problem I had was that there is either a rubber air hose or water hose/tube that runs just below the top of where you connect the spring loaded portion of the throttle position sensor and that is the reason I could not connect the throttle position sensor with the bottom portion of the throttle position center (the bottom of the T with the female electric connection at the bottom) to the right of center and move it clockwise to the left, because that approximately 3/8" rubber tube is in the way.

I guess simplistically, my problem is that I did not pass emmissions and NOx are too high. Tech said it could be due to my high idle in the 2000rpm range. Don't know if what is causing high NOx emmissions is also causing high idle and erratically fluctuating RPM up to 4000-4500 under load, and could possibly be related to throttle position sensor, EGR or something else. Just hoping to pass emmissions. I will try cleaning he EGR. Thank you for your suggestion and knowledge.

fixmiester

First of all, high no-load rpm will produce high NOx, and must be controlled by introducing EGR. If you do have a broken EGR tube, that would definitely cause a problem.
But your description of having a very high tach reading under mild acceleration, with no apparent increase in actual engine noise/RPM , is baffling. It's as if your tach is reading the output from the TPS! You sure you have things hooked up right? ECU issues may be contributing to the problem, but you're going to have to fix one problem at a time. Any codes being thrown?

sndlight

An idle hunt is an obvious sign of the idle air control valve bearings going bad. http://planetsoarer.com/IAC/iac.htm

However the rest of your problem is likely an EGR/vacuum leak (an egr problem is a vacuum leak). I dont think an ECU rebuild may help

dicer

Right on about the egr and why I suggested it. Vacuum leak can equal idle problems too.
The $600 plus IAC last a long time but can get dirty.

tyncobb

FIxmiester, sndlight and dicer;

Thanks for the comments and great article on the IAC. I think I will check a pick & pull yard that has a 92 LS 400 and try to pull both the EGR and IAC and then clean both as instructed and then attempt to install both cleaned parts. After reading Planet Soarer, it sure sounds like that is my problem with the hunting RPM's and idle so high. Hope to do that in the next two days and then will follow up with results. Thanks to all for your insight, experience and resources. Hopefully that will straighten things out so that I can go back and pass emissions.