HawkFanatic

iTrader: (1)

I have a 91 Formula 305TPI/5spd. It is mostly stock with 118K on it. I have owned it for about a year and put 5k on it. Since I have had it, when I start it, regardless of engine temp, it will idle a bit high, about 1100-1200, until I come to a complete stop and stay stopped for 2-3 seconds before it settles down to normal idle. I can deal with this.
The new problem I am having is that at start up, regardless of engine temp, the car will intantly shoot up to 2200-2400rpms for 2-3 seconds before settling down to the normal high idle, and then falling to normal idle after I stop.
I think these two are related somehow...

Everything is stock, except I replaced the AIC, and the MAP sensors. I also replaced the injectors with some South Bay stock replacements.

Other than these two minor issues, the car runs and drives great. I get about 22mpg average and plenty of power, but I do not like how high the revs are on a cold engine, so if anyone has any ideas, I would appreciate them.

TTOP350

iTrader: (8)

That could also be a tach tach filter issue.
Have you checked the rpms with a another tach?
also OHM the intake and coolant temp sensors ay diff temps to see if they are ok.

1991sleeper

iTrader: (-3)

Check the TPS .. Mine did similar about the 1200 until u come to a stop thing it was the TPS starting to go bad ... Also check the throttle linkage and make sure it closes completely and instantly every time u let off the pedal ... If not just put a stiffer return spring on it .... Also wouldn't hurt to clean up the throttle body with it running and a can a carb cleaner ... Might as well clean the MAF too while u got It all apart it seems like my MAF on my DD needs cleaned about every 6-7k miles .... Does it idle normal after this hiccup ?

HawkFanatic

iTrader: (1)

Ok, I know it has been forever since I started this thread, but I finally got around to checking the suggested items.

The Coolant temperature sensor measured about 6860ohms with the ambient temperature at about 44 degrees, so so far, that checks out. I will have to check it at operating temperature once the snow clears and I can drive it.

I also checked the TPS, and it showed .64v closed, and 4.32v full open. Are these value low? and if so, is it because the battery might be down a bit(11.6v) from sitting?

Ransford2987

It sounds like you have a vacuum leak/issue. I would check this: https://www.thirdgen.org/tpimod2
I would also make sure all of your vacuum lines that were disconnected are properly installed. I've created this situation before when I forgot to connect the brake booster vacuum line. It could be your IAC gasket is leaking or something related to the IAC, since that is essentially a vacuum leak into the intake. I'm assuming all of this happened when you performed maintenance?

bestracing

I have helped a little with this one and it has got me scratching my head as well.

1991sleeper, This car is a speed density TPI so no MAF

TTOP350: the motor is actually reving that high and returning back to idle like he said.

He used an ohm meter and checked the sweep of the TPS sensor and it doesn't look erratic. I think he's checked for vacuum hose leaks by plugging up the vacuum lines and no difference.

The coolant and air temp sensors are the next to be checked out when weather gets better. We've been through some nasty ice and snow storms in the past few weeks around here.

Ransford2987

I should have sent him this link for the TPS: http://www.iroczone.com/2009/10/adju...on-sensor-tps/
MAP cars should be .71 +/- .05 according to the article, which differs from the previous article, I know. Maybe someone with more knowledge can clarify?
My thought is this: if his minimum air speed is off and thus the IAC is needing time (2-3 seconds) to adjust, that could be his delay to bring RPMs down. Even if this isn't the issue, it's one more thing that you can check off that list and shouldn't have to do again. Plus it takes like 5 or 6 minutes.

Just my 2 cents here, replace those temp sensors. They are like $11 at AutoZone and probably cheaper online. So if you're waiting for the weather to clear up and you have some time anyway....

bestracing

I haven't a clue as to what the voltage should be at idle but the TPS being off would make some sense.

Hawk, I don't think the battery being a little low would throw off the TPS voltage since the battery voltage is still at 11.6 volts and the TPS voltage is regulated at 5 volts. You can unplug the TPS sensor and verify that you actually have 5 volts to the sensor just to be sure.