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Discussion Starter · #1 ·
HEY GUYS
THIS 1988 TPI UNIT IS DRIVING ME NUTS.THE INTAKE HAS NO SENSOR.
SITTING AT IDLE IT HAS A TENDENCY TO SURGE FROM 900RPM TO 1000RPM
THEN DOWN TO 900RPM AGAIN.WHAT DO YOU THINK CAUSES THIS???
HELP!!!!!!!!!!!

DON GREG
1ST.CAV
 

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It could be an air leak, check that all gaskets are in good condition and that all vacuum hoses are good.
Look at the fuel regulator on the passenger side at the rear of the engine, it has a vacuum line going to it - make sure this doesn't have fuel in it. If it does it means the diaphragm in the regulator has split and needs to be replaced.

What happens if you open the throttle a little ? does the surging go away ?
Sometimes the TPS (throttle position sensor) can go bad, which would cause the idle valve to fluctuate. Hook a volt meter to the tps and check its operation.

It could also be the idle valve, its circled in this picture:



This valve is controlled by the ECM, when the throttle is shut it allows air to bypass the throttle and enter the engine otherwise it would stall.
Is the throttle body clean ?get some carb cleaner and make sure its nice and clean, take that idle valve out and clean that too - if either get gummed up it can cause problems such as this.
Once cleaned you need to reset the idle and the TPS sensor, read this: http://www.thirdgen.org/tpimod2

The air leak thing is especially possible on a MAF car - if any air gets to enter the engine after the MAF the ECM gets confused. The MAF measures how much air goes in to the engine, from this and a few other things (RPM, temperature) the ECM works out how much fuel to squirt in. Now, if the MAF measures X amount of air and then more gets in after that the calculations the ECM does are wrong.. which the ECM notices and tries to fix, but it fails to do so.

Have you got rid of the EGR ? what about the EVAP valve ?
Does it drive okay ? power good ? have you checked for trouble codes ?

The thridgen site has a ton of info on this system.
 

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Discussion Starter · #3 ·
WHEN IT COMES OFF IDLE,IT RUNS EXTREMELY STRONG.IT ALSO SEEMS TO
BE RUNNING RICH,THE EXHAUST SMELLS LIKE RAW FUEL AT IDLE.

THANKS
DON GREG
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Exhaust leak will cause the O2 sensor to go whacked, causing rich idle..Sensor sees excess O2, and adds fuel to correct.
Also, if the runner gasket is on wrong, it will have a vac leak.
Need a scan tool to read the system.
 

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Exhaust leak is worth checking too.

If you haven't read the codes yet you should be able to get autozone to do it for you, alternatively if you pinout A and B pins on the ALDL plug and switch the ignition on the dash light will flash, its sort of morse code. e.g. the first code that will be shown is 12.. so the light will go "flash..... flash flash". One and then 2 right ? Each code is repeated 3 times.

Look here for a longer description and a list of codes http://chevythunder.com/fuel injection troubleshooting pg A.htm

List of codes with possible causes : http://www.iroczone.com/2009/10/decoding-ecm-trouble-codes/

Hope that helps
 

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And, turn off the caps lock.........
 

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HEY GUYS
THIS 1988 TPI UNIT IS DRIVING ME NUTS.THE INTAKE HAS NO SENSOR.
SITTING AT IDLE IT HAS A TENDENCY TO SURGE FROM 900RPM TO 1000RPM
THEN DOWN TO 900RPM AGAIN.WHAT DO YOU THINK CAUSES THIS???
HELP!!!!!!!!!!!

DON GREG
1ST.CAV
is this with a stock or programmable ecu?
 
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