I just swapped in an 89 L98 TPI. The engine will start and stay running as long as you hold the throttle open and keep it above 1500 rpm. It refuses to idle. But when the throttle is held open it runs and sounds great like there is nothing wrong. but when you let off it drops then chokes and dies. I have tried messing with the TPS and IAC nothing seems to change. There are also no trouble codes coming from the ECM. any ideas? thank you all. Jonny

When you let off the throttle what rpm does it drop to? Or does it die immediatly?

The rpms fall like normal then when it gets below 1500 it dies like it isn't getting enough fuel or air.

I just had the same problem with my 89. It turned out to be a vacuum leak. Found that out after replacing fuel pump and filter. Just my 2 cents though.

had similar problem with bad fuel pump. just saying.

Where was it leaking from? As far as I can tell I have every vac. port either plugged or hooked up....

Could the IAC be shot? how would I test it?

I had some leaking around the runners at the plenum and base. I thought I had everything tight too. As of right now it is surging and stalling until it gets warmed up. I believe that has something to do with either the IAC, TPS, or the EGR being stuck open.

I was going to make a thread on the exact same problem. So I decided to just add on.

91 Z-28 LB9

will start but no run... I just removed the TB and cleaned it out. Next am going to clean out the intake as there is plenty of build up their. I have a question on the IAC

I heard about testing the IAC is to remove it from the TB and hook the elctrical part of it back up. Then turn the car to the "on" position. w/'o starting it. check for movement in the IAC up and down. if no movement-could be bad IAC right? also-after i did the test I read a warning i should have read about the IAC. is that it may shoot out.

well, I performed this test and there was no movement so when I went to turn the key to the "off" position..out it went! so i found the spring and valve. but now when i put it back together it doesnt stay put. it is able to be turned by hand. Before it shot out I was unable to turn it by hand. as the TPI IAC are a little bit priecier than the TB I would like to get more life out of this IAC. Does anyone know if this one still might work... or should I just stop penny pinching and buy a new one?

i say but a new one lol, just my 2cents

so, all I have gotten out of this is that it could be my IAC, or MAF sensor, or fuel pump. (can't be the filter cause I just replaced it) I also have an adjustable Fuel pressure reg, that I have no idea what it is set to. any other suggestions?

just bought a new IAC 108 at NAPA.

Well, I am utterly excited to report that it was a bad MAF sensor.... then I cringe when I think of the whole now in my bank account... At least my car now runs strong right? So yes, the problem has been fixed, no more pulling of the hair in large fistfulls. Thank you everyone for your help, check out my page if you want to see pics of the MPFI V6 to TPI V8 swap. I am even thinking about writing up something for it.

Jonny B

Still in the rut..... Cleaning out throttle body, plenum(removed yesterday)(both full of build-up) found a vaccumn line that was not connected it runs uder the plenum it goes to the throttle body dont know where the other end goes yet...lol.. Anyway. I order gasket kits (out of stock), and will hopefully put it all together tonight if not sometime this week with the new IAC and everything cleaned up am expecting my car to be in driveable condition.

The other end goes in right before the coil, there are two ports, they are for the EGR switching IIRC.