Fluctuating Idle

[bigred88]

I recently did all of the "ultimate TBI" upgrades, including the porting. I also added a 1/4" spacer to the injector pod. The porting and the spacer are the only things done between when I had a normal idle, and what I have now, which fluctuates on a cold startup. After the engine warms up, it runs fine, but I would say it goes anywhere between 700 and 1500 until its warm (just a rough guess, I don't have a tach). I also put on a different fuel pressure regulator- which is what my instincts tell me is the problem.

So- can a faulty fuel pressure regulator cause a fluctuating idle? Or is there something else that stands out to any of you with more experience than me?

Thanks.

 

[Stomis]

Ya know I'm hangin in there for you to get this fixed. My 88 camaro did the same exact thing when I did the ultimate TBI mods. Thats why I only did the spacers on the truck...

 

[bigred88]

Well, I still have an unmodified TBI, so if that is the problem, I can just switch it back, but I like the performance increase I got from the mods...

 

[kd7kmp]

Check for a vacuum leak...A spray bottle of slightly soapy water is a great way to check for a vacuum leak. Spray it all around the base of the TBI unit with everything in place and hooked up. Check all you vacuum hoses. If they are more than a few years old check then for cracks, etc.

A misaligned gasket or something caught between the mating surfaces will cause an erratic idle. It is possible that you damaged the TB unit with doing the TBI mods...double check everything you did, make sure the mounting bolts are tight and that the gaskets are properly aligned.

 

[Thunder]

Sounds like a vacuum leak to me too. Did you use a new base gasket?
I have had base gaskets go bad. Rough or hunting idle is usually the symptom.
What king of FPR did you install? If it is adjustable you really need a guage to set the pressure.