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Can I rebuild/clean my IAC & TPS? ***ideas to fix stumbling***

K

KRAZIE87K5

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I've got surging issues at idle with my '89 Burb. First thing I am going to do is attempt to rebuild and clean the IAC and TPS. Things that are new... cap, rotor, wires, plugs, fuel filter. No EGR, the Edelbrock intake I have doesn't support it. EGR shouldn't matter at idle anyways... The TBI has been sitting around for nearly 1 year without running. I'm sure its yucked up (technical term) inside.

Any thoughts?

-Dan
 
Re: Can I rebuild/clean my IAC & TPS?

IAC can apparently be cleaned out, as can the passage in the throttle body. Haven't had mine apart yet. You may need a "special" deep well socket to get it off. Mine (TPI) won't come off with a crescent wrench, I'd rather not break the plastic connector trying to remove it.

TPS I doubt you can clean, but perhaps soaking it in some electrical/plastic friendly cleaner, and working it while its submerged, might help remove any buildup inside. I really don't know how they work (guessing its like the fuel sending unit) but when they go bad, they tend to get "dead" spots in their travel, where voltage drops to nothing.

There was just a thread on adjusting/setting the TPS properly, might want to search for that.

A scanner and manual will help you check these items out, since IAC steps are typically displayed, as is throttle open position based on TPS readings.
 
Re: Can I rebuild/clean my IAC & TPS?

The TPS is like 20.00 at Autozone. It looks like a sealed unit I would just buy a new one.

tim
 
Re: Can I rebuild/clean my IAC & TPS?

1989 CHEVROLET TRUCK V2500 3/4TON SUB 4WD 8 Cylinders 350 K 5.7L TBI

Qty.
Item
Description
Part No.
Avail. Core Value Unit Price Sub
Total
IDLE AIR CONTROL VALVE WELLS
AC102 $0.00 $33.99 $33.99


AutoZone pricing off their site! /forums/images/graemlins/wink.gif
 
Re: Can I rebuild/clean my IAC & TPS?

Dan,

Yes you can clean it, but you can't rebuild it. It's not rebuildable. I will see if I can find the post that I used to both adjust and clean it. The TPS is not rebuildable, but the IAC is cleanable.

Here is the link is used from the Camaro board on Thridgen.org

Cleaning/Adjusting

This is for a TPI system, bit the TPI and TBI's are almost the same.

Good luck.

Rob
 
Re: Can I rebuild/clean my IAC & TPS?

Thanks Rob! That link is perfect. I will do that tonight, and post up if it cures my surging. You da man! /forums/images/graemlins/cool.gif

-Dan
 
Re: Can I rebuild/clean my IAC & TPS?

Ok I replaced the IAC, and set the TPS which was off a little. I set the idle position at .540vdc exactly, and WOT = 4.434. It seems to cycle from idle to WOT without any gaps, jumps, dead spots, etc.

I bought a vacuum gauge, and found that @ idle the engine is making 20lbs at the vacuum canister against the firewall. I then noticed that the vacuum canister at the core support (drivers side, near the front bumper inside the fender) was NOT CONNECTED! I reconnected while the truck was running and strangly enough the idle dropped about 100-150RPM. /forums/images/graemlins/confused.gif I'm not sure what that was about... also, it did not change the vacuum at the canister near the firewall. I connected it to that other canister... I think it needs to connect to the lower right vacuum port on the front of the TBI (ported vacuum). /forums/images/graemlins/eek.gif /forums/images/graemlins/eek.gif /forums/images/graemlins/eek.gif I'm going to go correct that NOW! Whoops. /forums/images/graemlins/blush.gif

Regardless, the damn thing still does something funny at idle. Its almost like its missing... the engine lurches (loss of power) and then regains its power right back. Very wierd. But no more stalling since I bumped the idle up a little with the set screw at the TBI. I DID the whole ALDL paper clip in A + B, wait 30 seconds, remove the IAC plug, start the motor, bring the idle to 450RPM. Instead... I set it at 600. No more stalling = GOOD.

SO... having said all that long winded junk... what do I look at now?

Thanks all!

-Dan
 
Re: Can I rebuild/clean my IAC & TPS? ***UPDATE*** No go...

Dan,

I will try to lend some insight, but keep in mind I run a TPI and am not sure if the issues are the same and or the resolutions the same.

I will give you what I know, and what I have heard and or tried myself.

First, fuel pressure, check it and make sure the filters are not dirty or blocked.

MSD box, if you are running one bypass it, I had this problem.

Check the distributior module. Look for more vacume leaks, these things are killers to FI motors.

Check the timing with est sensor and go back and reset it. Have you changed anything new on the motor. The idle and everyting is based on the chip in the module.

Oil pressure sending switch, sometimes this screws with the computer.

Last but not least, surf the Thridgen.org board under the TBI sections, thoes guys on that board are real TBI geeks, and have done everything and or tried everything to TBI engines, just don't tell them your motor is out of a truck if you post, otherwise they won't even talk to you.

Good luck.

Keep us posted.

Rob
 
Ok... so I went ahead and set the timing back down to 4* from 11-12*, and BANG... the darn thing runs like a top. Go figure?!!! To explain myself... I have a '96 block in the Burb, and the timing cover only displays the 0* mark. The motor DOESN'T run well at 0*, so I tweaked it up a little higher! /forums/images/graemlins/blush.gif Well now with a new IAC, timing set to 4*, and the idle set correctly, its happy!

Just thought I would post up what fixed the problem! /forums/images/graemlins/wink.gif

-Dan
 
Did you remember to unplug the wire that disables the computer timing retarding? Becuase I think my 88' runs at about 4 degrees BTDC with the wire plugged in. Anyway, glad to hear she's running good again.
 
I did actually pull the timing connector, yes. Thanks for putting that up though. I love seeing all the info out here for folks to learn on their own from the mistakes that I make on my truck! /forums/images/graemlins/blush.gif

-Dan
 
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