Strange Idle Surging

[davehaynes1]

First off i have a '93 3L V6 Manual

So last week my truck would'nt start. turned out to be a fuel pump issue, no power.
I removed the fuel pump relay as i suspected this to be the issue and hotwired the fuel pump as a temp. fix.
Then a couple days ago i put the fuel pump relay back in to test it and everything started working again.
While i was running the truck with the fuel pump hotwired i started getting an idle surge and now with the fuel pump relay back in i still have an idle surge.

When i start the truck its fine, sitting at about 1200 as it warms up, its not untill i drive for a little bit and then depress the clutch that the surge starts. dropping between 0-1000 and often stalling.
Truck drives fine, no hesitation or lack of power.

please guys any help!!

 

[Bad_Vision]

Sounds like a vacuum leak or the idle air sensor.
Start by smoking your lines to test for leaks if you have no leaks then move along to sensor testing using a ohm meter

 

[Bad_Vision]

Also look into the fpr on fuel rail because of that gets junk in the diaphragm it can cause fuel surge.

 

[davehaynes1]

Don't think I can afford one of those fancy smoke machines. I'll give my lines a check over later and use the carb cleaner technique

 

[davehaynes1]

Oh yeah, I forgot to mention.
I have a pretty nasty broken exhaust, before the 02 sensor. I know in theory this can cause an idle surge, but the exhaust has been broken for about 3 weeks and the surge has only occurred this week since the fuel pump relay issue.

 

[Ahlem]

You don't necessarily need a fancy smoke machine. You tube shows a guy with a big breath and a cheap cigar. Others have made their own for about $20
I'm having a similar issue and have it narrowed down to temp sensors. Unfortunately I haven't figured out exactly where they are all located. I believe there are three of them. The forum is a bit skinny on this topic.

 

[davehaynes1]

Well today I swapped out my fuel filter for a brand new one and then pressure tested.
Fuel supply is fine. Sitting around 38psi on idle and climbing to around 45/50 while driving.
Please guys this is driving me crazy now!!

 

[The Count]

One thing you should consider is your base idle speed when the motor is warm. If the base idle speed is to high the computer will try and lower it, and that will cause a surging or cycling idle idle condition. The same can apply to too low of an idle speed, though that would likely also cause a stalling condition at least sometimes.

If the base idle is fine I would start with the basics and try and elimate possibilities like....

-Vacuum leaks ( listen for them and block off sections and see if the condition changes)
-Base timing
-bad/out of range sensors (focus on ones dealing with coolant/engine temp)

I would also want to verify that the condition starts when the PCM should be switching from open to closed loop. If that is the case, that would verify that the computer is seeing a problem it is essentially trying to fix, by changing idle speed or adjusting the injector pulse. It would also throw suspicion on your exhaust leak, since the PCM is essentially ignoring o2 reading until it switches to closed loop.

Someone may be able to guess at what MIGHT be wrong with your vehicle, but no one can accurately diagnose (especially pre-obd2)car problems over the internet. If they could, people like me would be out of jobs. It's gonna take some work on your part if you want to fix this issue without paying someone to do it for you.

 

[davehaynes1]

I tried to run a scan on it yesterday but i have no power to the plug.....
I also had no CEL so i pulled it all apart today and i had a dead bulb, ive put a new bulb in now and my CEL is on with ignition and not illuminated when the engine is running.... this means i have no codes right??