jac113

iTrader: (4)

Hello all,
I'm trying to hunt down the cause of my high idle problem without buying all new parts and am down to a few items. TPS, EGR and vacuum leak at throttle body. My car is a '92 with a 5.o tpi/5speed.

The TPS checked out some time ago on the scanner. max volts was at 4.3 and min was at .6-.8 with not volt spikes. It's non-adustable so it is what it is.

The egr when removed will hold vacuum if it's compressed and the port is plugged. When release it will go back to original position. It looks pretty clean too.

I'm wondering if I remove the vacuum line from the egr and plug both ends if the enginewill run as if it had no egr. I want to do this to see if the egr is causing the problem or will just plugging ports and not blocking off the intake will cause other problems, besides and SES light.

I just set min. air this weekend and when I unplugged the IAC the engine idle surged like crazy which kinda made it hard to set. Does that idle surge with IAC unplugged indicate a bad egr? Idle rpm is about 750.

thanks

vetteoz

iTrader: (13)

Disconnecting the connector on the EGR solenoid will prevent EGR valve operating

jac113

iTrader: (4)

Good idea, dnt know why I ddnt think of that. On my short drive home today it started to idle at about 1100 but would calm down once I throttled it. Seems like a sticky egr or throttle plate not closing as it should.

I'll unplug the vacuum solenoid and see how no egr effects idle.

Thanks

jac113

iTrader: (4)

update:
I unplug solenoid this morning and I noticed a humming noise from inside the plenum, kind of like a turbulent air sound or when you route the smog pump hoses wrong. Anyway I take an alternate route to work so I could drive it a couple of extra miles and I immediately notice a small power gain. Hopped on the freeway and it felt even better. I get off and pull up to the light and the rpm slowly returned to 750. Came to the next light and it got stuck at 1100+. Throttle it and it came down to normal.

Long story made short, the egr may not be the problem. I'm thinking it may be a bad throttle body and/or tps.

any ideas anyone

90vertiroc

The TPS checked out some time ago on the scanner. max volts was at 4.3 and min was at .6-.8 with not volt spikes. It's non-adustable so it is what it is.



The TPS is adjustable here is how:
Throttle Position Switch (TPS)


Tools needed:

1. [*]
2. [*]
3. [*]

Turn on ignition, but don't start the engine.
With a scanner: plug in the scanner and read the TPS voltage. It should be 0.54Volts +/- 0.075Volts
With VOM and jumper wires: disconnect the connector from the TPS. Using your jumper wires, make a connection allowing some room for the VOM terminals to contact the jumper leads and read the TPS voltage.
If out of spec, loosen the two screws holding the TPS to the throttle body, and slightly rotate the TPS up or down, reading the voltage until it comes into specification. Tighten screws. Using the throttle lever, rotate the throttle to WOT (wide open throttle). The TPS voltage should be over 4.0 volts. Close the throttle again, and then slowly open it to WOT, observing the voltage reading. It should increase progressively and in a linear fashion. If it sticks or jumps or falls off at all while doing this check, that could mean a bad TPS switch and could be a cause of stumbling and driveability problems.
After setting the correct voltage, turn off ignition switch. Remove jumpers/scanner and reconnect the TPS connector as required.

jac113

iTrader: (4)

thanks 90 vert but i believe the 90+ tps's are non adjustable b/c of the two fixed screws which leads me to believe that base starting voltage, although not always the same, is just a base and the computer compensates from there. I've verified this with a scanner some time ago. The car would have about the same idle rpm with different closed throttle voltages on different start ups. I've noticed voltages at start in range of .67 to .88.

i'm thinking it has to be a leak at throttle body or a bad throttle body itself considering with or w/o the egr it runs pretty much the same.

thanks

jac113

iTrader: (4)

Hey guys,
I just want to throw a couple of things at you before I kill this post. I did a couple of things over the weekend to help solve the high idle problem and wanted to get an opinion. I went to the junkyard and bought a tps from an '87. It looked non-adjustable at first glance so I took it home and realized it was adjustable. I put it on and started the engine and the idle would bog dog when accelerated. I adjusted the tps by ear, took it for a drive and still had the high idle. I adjusted the tps to lower the idle and the idle still manage to climp to 1100.
I then took out the IAC to clean it even though it's only about 2,000 miles old and to set the pintle at the proper length. When I drive the car now the idle still hangs and will stay at 1100, BUT if I throttle the gas while decelerating the idle will return to normal when I stop. It works every time for some reason.
Would this be a bad IAC valve. I'm thinking it's getting stuck somewhere on the idle return.

Any ideas?

santis5

Yes, check that your throttle linkage is returning properly. It could be binding when you lightly let off the gas but when you open it all the way then release, it may be returning properly. I can't tell you how many times people start changing things only to find out it was a simple fix all along.

jac113

iTrader: (4)

good point, i can't dismiss that one. Everytime that i've checked for a sticky linkage or weak return spring i've always jerked the throttle but never really simulated a real acceleration or slow opening. Will check that next. thanks

90vertiroc

]

ASE doc

Worn throttle bushings are a common problem on GM cars. This can cause an inconsistent idle and other driveability issues. Check the throttle shaft for any lateral movement. Hold the throttle arm firmly and try rocking it up and down, back and forth. It should have almost no movement. Look for unusual movement in the shaft. If close inspection reveals worn bushings, replace throttle body.

jac113

iTrader: (4)

awesome ASE,
I did notice some time ago that my idle would change even though the idle shaft was resting on the idle screw. I rotated the shaft more and the idle would drop. I haven't been able to duplicate that issue so I kind of forgot about it. I was just checking the TB yesterday to see if my blades were loose but didn't check the shaft for play.

i'll add that to my list.

thx