Isuzu SUV Forum banner
1 - 6 of 6 Posts

·
Registered
Joined
·
38 Posts
Discussion Starter · #1 ·
I have a surging idle when cold, cool, or just been sitting for a while. It idles low (around 500), then surges between about 750, and almost dying, running very rough. I can put it in gear, and by the time I reach the end of the driveway, it's OK. After it gets warm, it idles fine. Any suggestions where to start looking? It's had injector cleaner and almost all new vacuum lines installed.
 

·
Registered
Joined
·
155 Posts
I have a similar problem. I have a '90 Trooper with a 2.8L V6. I didn't have these problems until I started screwing with the TBI. The TPS being adjusted improperly will cause this. To test your TPS, pull out your voltmeter and get ready to probe.

On your TBI, locate the TPS. It is on the opposite side of the TBI casting from the throttle linkage. Where the other side of the linkage sticks out of the TBI, there is a 3 wire sensor. Stick the positive lead into the center wire on back of the connector. Ground the other lead from your multi meter. With the ignition on, but not running, the TPS should read .5 volts. With the throttle in the wide open position, it should read 4.5 to 5 volts.

The IAC motor is the sensor that screws into the TBI with a square four wire plug. It has a pintle that moves in and out allowing more or less air into the fuel/air mixture. If this is bad, it should be replaced. I believe they are about 30 bux at Advance Auto.

You might need to adjust the idle screw on the other side where all the linkage hooks up to the TBI. There is a plug that covers the idle screw so you can't adjust it, but you can pop the plug with a nail and a hammer and pull the plug out which gives you access to the idle set screw. Turn it up just a hare and try it. Keep doing this until the idle stops dropping below 700 RPM.

Do you have a check engine light coming on? If so, what is the code?
 

·
Registered
Joined
·
38 Posts
Discussion Starter · #4 ·
No CEL, and my first suspicion was the IAC, if they had one. My Superduty had one go out, and they won't idle at all. I did not know where this one was at, or if it even had one, as I'm not too familiar with the Isuzu's yet. I don't think it is the idle speed, as when it's warmed up, it idles a little over 1000 rpm in neutral, and around 750 in gear. I'm afraid I don't know what TBI and TPS stand for. I'm assuming "throttle body" and "throttle position". Strangest throttle body I ever seen if that's what it is...

Thanks for the info.
 

·
Registered
Joined
·
2,184 Posts
have you checked for loosed or cracked vaccum hoses, a little suction leak can give you a big headache
 

·
Registered
Joined
·
38 Posts
Discussion Starter · #6 ·
Yeah, and I replaced almost all the vacuum lines (only took 237 foot of hose). Some of the hose looks original, and is of an odd size and doesn't fit real well. I'll do some more checking. It actually didn't start this idle problem until I replaced the hoses and got the idle down from 1500 to 1000. Now it's back up to around 1250. I may just drive it...
 
1 - 6 of 6 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top