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91 slight surge

A

Alex

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Hi all, I get a slight surge (down from idle) when I'm at a stop sign. It does not occur when the truck is cold just when it is warm. Besides that, the truck runs great but I cannot seem to find the problem. The cap/rotor/plugs/wires/injectors are fine. Any idea what may be wrong? Thanks in advance. /forums/images/graemlins/thinking.gif
 
I would check the EGR valve... /forums/images/graemlins/thinking.gif
 
my 91 sub acted similar (along with a few other issues) and finally threw a TPS code. As i'd changed it less than 2 years earlier i didn't believe it, and finally DID change it.
That resolved all my issues and runs great now! Even seems to have picked up the mileage a bit! /forums/images/graemlins/shocked.gif
/forums/images/graemlins/burb.gif /forums/images/graemlins/thumb.gif
 
First check for trouble codes and repair any problems.
If there are no trouble codes:
Check all your vacume lines and Throttle body gasket for leaks.
Pull off your EGR valve and clean it out with carb cleaner.
Wouldn't hurt to pull and clean off the IAC valve either.
As said in above post a faulty TPS can cause surging also.
 
Not meanin to hijack your post, but, in my 87 i have a surge at idle, sometimes feeling like its gonna cut off. When it gets warm, is when it does it, but it doesnt do it everytime. Same thing with when i get on the gas from a full stop, feels like no power and almost a miss, but it doesnt do it everytime. Could this be a TPS? Everything on the ignition minus the distributor itself was changed in january or early feb. If this could be TPS (i havent had time to check for codes yet) where is it located? Anyone have a pic? Is it hard to change? About how much does it cost? Thanks.
 
Ok there are no codes, all the plugs are clean. I broke a plug so when i go to autozone to get one i might go ahead and get a TPS and look for it on the truck as i have no idea where it is or what it looks like. Should i get one for an 87 or an 89 (engine), if they are different pn's?
 
TPS plugs into pass side of TBI. A couple small bolts, and a slight range of travel for adjustment on it. It almost reminded me of those old manual choke covers.
I think they run around $30.
 
be sure to check all the sensors, but also check the wires. I had a surge, and my O2 sensor wire had the insulation stripped off, with a wiring harness crossing it, right where it was stripped. the voltages jumped around, sending wierd readings to the computer
 
Hey my truck does the exact same thing. Mine gets worse when the a/c is kicked on. I have already done the TPS (I did get a low TPS code before, now it doesnt) and done a full tuneup. I replaced a half dozen bad or suspect vacuum lines. It runs better, but I still have this surge of about 100 rpms. I am getting an EGR code, so that is the next thing coming off for inspection
 
You may end up having to "adjust" the TPS if you get a new one anyways, might I suggest making sure yours is working correctly before throwing $30 away?

I'm sure a search on here or google will yield TPS test procedures.
 
My 91 does the same thing. I'm pulling 21 vaccum, replaced ignition with MSD coil, 6a box, super conductor wires. Checked the TPS with multi-meter according to manual. No codes. I guess the EGR is the next thing to check. Thanks guys.
 
oops, almost forgot. One other thing on that was to clear the computer (batt disconnected for a few minutes), once the new one is in place, KEY ON (NOT STARTED), and give the accel a FULL cycle - idle to WFO and hold briefly, then key back off. Supposedly allows computer to LEARN the full TPS range.
Not sure if it was the new sensor that did it, or the re-programing??? Either way, much better now!
 
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