Almost stalls on cold start, then runs fine?????

[99vipersnake]

Hey guys. New to the forum and already have a question. I have a 99 roadster with ~30k miles. I have this issue when I start it cold (let it sit overnight) and start the car, the rpms will drop down to where it will almost stall (it has also stalled at times), and then they will immediately jump back up, and everything is normal. No issues at all after this, drives normally, idles normally...It does this every time I start it cold. I've cleaned the IAC and tested the pin inside (it came out when I turned the ignition on, but I couldn't turn it back by hand, so I reinstalled it, and it wound itself back in), tested the TPS voltage, and installed a brand new battery. Could it still be the IAC, even though it looks to be working fine, and it's idling fine after start up?
What else could cause these symptoms? Vacume leak, map sensor, temp sensor (how can I test these sensors)? I have no error codes. Car runs perfectly after start up, it's just this low rpm hickup which is kind of annoying...

[scottyitsk]

Originally Posted by 99vipersnake

Hey guys. New to the forum and already have a question. I have a 99 roadster with ~30k miles. I have this issue when I start it cold (let it sit overnight) and start the car, the rpms will drop down to where it will almost stall (it has also stalled at times), and then they will immediately jump back up, and everything is normal. No issues at all after this, drives normally, idles normally...It does this every time I start it cold. I've cleaned the IAC and tested the pin inside (it came out when I turned the ignition on, but I couldn't turn it back by hand, so I reinstalled it, and it wound itself back in), tested the TPS voltage, and installed a brand new battery. Could it still be the IAC, even though it looks to be working fine, and it's idling fine after start up?
What else could cause these symptoms? Vacume leak, map sensor, temp sensor (how can I test these sensors)? I have no error codes. Car runs perfectly after start up, it's just this low rpm hickup which is kind of annoying...

big engine, cold start, normal.

[99vipersnake]

Is that really normal? I've had other cars with big engines (not 8 liters, mind you), and all of them started normally, even when cold...

[Curz]

mine never does that. It actually runs best cold - as far as idle RPMs

[scottyitsk]

mine did the same thing when i was stock and not tt.. it still does it tt.

it probably has to do with the Idle Air Control ... possibly

[99vipersnake]

Originally Posted by Curz

mine never does that. It actually runs best cold - as far as idle RPMs

well. mine idles great as well, it's just right after cranking, the engine really bogs down, quickly recovers, and then everythings hunky dory. It all takes about 1-2 seconds. I have no other symptoms except for this particular starting issue.

[Netko]

Have you changed the plugs and wires? That is what needs to be done at the 30k mark.

[99vipersnake]

no, but wouldn't the engine run/idle rough during normal driving conditions, if the plugs/wires are bad? Engine only briefly bogs down when it's been sitting for several hours. I've considered the fuel pump, but I've tried priming the fuel lines by turning the ignition off and on before cranking, and it does the same thing...

[dave6666]

With mine it was the tune. But if you are running the factory tune then the other stuff that was said. Plugs, wires, O2 sensors, IAC, blah blah.

[1.8t]

Mine has never done that before.