Hi my tpi 305 at initial start will start then immediately lose rpm then slowly build them back up or die completely. Then the next turn of the key it fires up and runs/idles fine. I’m thinking its a vacuum leak but was curious if anyone knew a good place to start looking?

 

Does this occur when the engine is cold, after heat soak, or under any circumstances? What year?

 

Vacuum would be a good place to start (spray throttle body cleaner around the base of the intake/plenum area/other areas where parts connect/gaskets present or wave a unlit propane torch in those areas and see if RPM spikes). I had a very similar issue that I just finally resolved with my 88' GTA, on cold start only the car would start good, idle would climb as its supposed to but within a few seconds it would stumble down and unless you quickly hit the accelerator it would die. On immediate restart the car would start and idle down perfect...it was very frustrating but I found a deal on a NOS AC Delco re-man ECM and decided to give it a shot (worst case have a quality back up) and it cured my issue completely. Another thing that can cause issues on these is a faulty MAF, mine was a real pain there because it threw no codes and on hot start up only would cause the car to start very rich because of a heat soak issue, I had a good mechanic figure that out while it was on the scanner and after replacing with a Delphi MAF that corrected it. A factory service manual is a real bonus with these cars for trouble shooting following the tree diagrams.

 

It’s a 87 and when it’s cold

 

If the SES is not on while running, there are probably no error codes present to provide clues. I'm presuming there are none since you didn't report the light being on. Basic items to check are vacuum hoses, PCV valve, throttle body cleanliness including the IAC, distributor cap and rotor condition, and spark plug condition. Those should be part of normal routine maintenance anyway. Among the first suspicions might be the IAC becoming sluggish.

It may be beneficial for diagnosis to alter the starting routine. After inserting the key, turn the switch to the RUN position for about two seconds before starting. While in the RUN position, watch the SES lamp action. The light should turn on for about half a second, then turn off for about half a second, then turn back on and remain on until the engine is started. If this does not occur there may be ECM, connection, or wiring problems.

During this first two seconds the fuel pump should run a prime cycle, and this is usually audible. If the pump does not run during this period longer cranking times may result. Also during the first two seconds the IAC should move to an open position if the coolant temperature is below 158°. This may not be audible from inside the vehicle, but allowing a little time for the IAC to retract might make the intial start a little easier since the IAC would already be a little closer to an appropriate position for a cold start.

 

Sorry I didn’t mention it, but yes the check engine light is on I haven’t had it scanned yet, I did what you said and waited a few seconds before trying to start and it started up fine. Honestly I’m not trying to spend any more money on this car, I’m hoping to put it up for sale soon. It’s pretty rough and I didn’t really know what to look for when I bought it, but after already fixing several things I doubt I’ll get what I’ve got in this car back out of it.

 

So I started up the car and let it idle all the way up to operating temp and the car started idling up on it’s own to around 2k rpm. I shut it off and it went right but to 2k, shut it off again and restarted it and it idled less than 500 rpm and roughly. I’ve put a new tps sensor on and adjusted it properly. The car also seems to want to over heat if just idling, even though I’ve flushed the coolant, changed to a lower temp thermostat, and both fans work. The gauge could be reading wrong though.