Alright everybody, i've got a motor swap project going with a TPI setup, i've heard of this problem, but havent heard of an answer as of yet...

The car starts fine, and runs, revs decently and such. Problem is, while at idle, the idle isnt smooth, it will run at 750-800rpm, then drop down to like 200rpm, and then back up...it seems to do this multiple times, sometimes even causing the car to stall. The wierdest part, is that when i put it in drive, the idle stays constant and doesnt have this problem.

It seems like its doing everything right, i start it up and it keeps the idle at about 1000rpm, then drops down to around 700-800(tries to at least, due to rpm drops).

I noticed through my scanner tool that it is in open loop operation and i have yet to see it go into closed (also my SES light stays on? possibly because open loop?) I'm not getting any error codes, and if i rev the car to 1500rpm or more it runs real smooth and sounds good.

I hope somebody out there can help me, i've tried so many sensor unplugs and such, but nothing seems to have solved the problem.

 

Aquikgmc,

I have had similar problems in the past. This is what I would do...

1) Check the fuel filter.

2) Check the Idle Air Control Sensor (make sure it is clean and
not compressed and/or full of carbon).

3) Check each fuel injectors' resistance with an ohm meter
(each result should be very close to the rest).

4) Check the fuel pump.

I doubt if 1 is your problem, but a clogged fuel filter can cause headaches. I would check it just to be on the safe-side. I have had tach jumping, like you described, from 2, 3, and 4 on my TPI motor.

Hope this helps.
Good luck.

 

The fuel pump and the fuel filter are brand new (so i'm not too worried about that being the problem, is there any easy way to get the IAC out? Its kinda in a hard position to get to and mine seems to be stuck in there pretty good. it idles at 1000rpm, then drops back down so is that a sign the IAC is good? or could it still have problems? My computer shows me the "ticks" or whatnot of the IAC, and they seem to change as i adjust the idle screw.

I'll check the injectors ASAP and let you know if i come back with anything wierd.

 

Well i pullled out the IAC today and it was dirty, so i cleaned all the carbon off it, it wasnt compressed or anything though, but car still having the idle problem

 

Did you get a chance to check the fuel injector resistance?

 

nah, i havent yet, hopefully i'm gonna do that today. I started thinking maybe my o2 sensor could be bad. The car still hasnt gone into closed loop, even after running a good 10 minutes. My scanner also reads a lean condition(no codes though) so i'm wondering if the o2 is bad, i'll check the resistence first though.

 

What year TPI? (S/D or MAF?)

 

it's an 87 MAF setup, 305 engine. didnt get a chance to check the resistence, i'll check tommorow

 

*sigh*

Well i tested the injectors all of them seemed to have good resistance, all very close to each other also. Did a compression test on all the cylinders, all good numbers.

I swapped in a different o2 sensor(out of a truck i had), and the mVolts seem to be way different than the previous one. Anybody know what they're supposed to be around?

Non-the-less, idle is still bad, im wondering possibly if my injectors are dirty or something, i'm gonna call a couple tech lines tommorow and run some injector cleaner through it in hopes that it will help, so the drama continues

currently we're thinkin the system is possibly lean somehow...more updates as soon as i get'em

 

Well i spent a couple hours on it this morning. I put a new o2 sensor, no good, so i poured some injector cleaner into the tank, no good...as i was adding transmission fluid to it something made me think...

My MAF has just been hooked to the front of the intake, and...i noticed that my fan was blowing air close to my MAF. So i pull up my MAF so its pointing up and away from the fan...DOH! idle smooths out...i let it run for awhile like this and it seems WAY better, all i can say to myself is

If i have any more problems i'll be sure to ask here, thanks everyone for the help

 

You'll want to get a filter and duct in front of that MAF, just like the factory installed.

 

i just got finished fabricating one using an impala SS lt1 box/filter, i just gotta get it mounted, should work good.