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Idle and decel AFR problem (tps?)

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williillii

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Discussion starter · #1 ·
So about two months ago I destroyed the motor in my GST.. I put in another one and ever since Ive been having what seems like TPS issues. For the most part the car drives fine. But when I let off the gas say at 2500rpms...the AFR will drop to ~12:1. Before the car would jump to ~17:1 and then read LEAN on decel.

I wouldnt really care but its screwing with my fuel trims real bad. When Im slowing down with the car in gear, since its running at 12:1 it tries to lean itself out. So when I take it out of gear and it starts to idle the AFR is really lean (16-18:1) from the ecu pulling fuel. It will do the same thing when switching gears depending on how fast I shift. Ex: when I shift from 4th to 5th just cruising, it goes 12:1 when I let off the throttle and then right when I get back on it it runs at 15.5ish for a second before it richens back up causing a hesitation.

Another thing to note is that when I decelerate from about 4-4.5k rpms, it will do its thing like normal, and then right around 2200-2000rpm it will jerk and go all the way LEAN like it shutting the injectors off like its supposed to. But as soon as I see the gauge jump lean it starts jerking and then runs rich again.

Ive tested the TPS every way I could find and it seems ok. Resistance is in spec. I pulled the throttlebody and set the TPS with a feeler gauge (.45mm) twice to no effect. When the throttle is closed the idle switch circuit is closed. As soon as I put the feeler gauge in it opens. It takes about a 50mV rise to open the switch. I probed the harness while its powered, and the TPS reads 4.96V when opened all the way.

Is there anything else I can try or should I just bite the bullet and replace the TPS to see if it helps? Also, is there a pin at the ECU I can check to see if the idle switch circuit is in good shape?

THanks!!


TLDR:

car runs rich on decel, then lean when comes to idle.
seems like fuel injectors arent shutting off
tps adjusted correctly, tests fine.
 
#2 ·
You have the same problem I had! DSMlink fixed that for me, but here is how to set the idle switch correctly on the tps. Put the feeler gauge inbetween the throttle stop. Then connect your ohm meter to pins 4 and 3. Move the tps all the way counter clockwise. Your ohms meter should read 0. Slowly turn it clockwise untill it reads infinity. At this point you are done. Tighten down the bolts and make sure the readings didn't change. Then take the feeler gauge out. You can then move the throttle plate by hand. It should turn from zero to 1 (infinity) when you barly move the throttle plate to open.
Hope this helps.
 
Discussion starter · #3 ·
spyder79 said:
You have the same problem I had! DSMlink fixed that for me, but here is how to set the idle switch correctly on the tps. Put the feeler gauge inbetween the throttle stop. Then connect your ohm meter to pins 4 and 3. Move the tps all the way counter clockwise. Your ohms meter should read 0. Slowly turn it clockwise untill it reads infinity. At this point you are done. Tighten down the bolts and make sure the readings didn't change. Then take the feeler gauge out. You can then move the throttle plate by hand. It should turn from zero to 1 (infinity) when you barly move the throttle plate to open.
Hope this helps.
Click to expand...
Well thats exactly what I did. I did it about 5 times with the throttlebody still on the car. And then I pulled it off and have tried setting it twice more and it doesnt seem to change a thing. I am pretty sure it is set correctly but I guess I can try again. Thanks.
 
Discussion starter · #5 ·
Hey man thanks alot...I guess Ill go play with it some more and see if I can make it work :D thanks.

As for pin 87...I should just check for continuity between that and the ecu ground? Or the sensor ground?
 
#7 ·
Most likely your idle switch isn't working properly. You can simulate this in DSM/ECM link if you have it. Otherwise, follow the steps above and you should be in good shape.

Also, make 100% sure you do not have any boost leaks or have any exhaust leaks. These will completely screw your A/Fs.
 
#8 ·
The TPS could be bad, I had one that I thought was good but replaced it and my problems went away. Could be the seals on the throttle body, have you replaced the seals with the chicago rawhide seals? And you can get a rebuilt TPS for a 1G for $25 from this guy http://www.throttlebodys.com/DSMTBs.htm scroll down and click on dsm sensors, gaskets, blockoff plates.

Here is the direct link for adjusting the tps http://www.plymouthlaser.com/tps.htm
 
Discussion starter · #9 ·
^Thanks but I have a 2g. Its a different animal when it comes to the tps and idle switch.

Today Ill try to readjust it for the 2342349th time and see if that helps. also Ill test the circuit.

I do have a small leak out of the rear facing throttle body seal. But I dont see how that will prevent the ecu from shutting off the injectors when its supposed to. The leaks at the throttlebody seals are so small I dont know why everyone makes a big deal out of them...Ive had much worse leaks that weren't even really noticible. This is definately an idle control problem and not a boost leak issue. Thanks
 
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williillii
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