Hi,
i have 91 camaro with 305TBI stock as far as i know, i add only open element. It runs quite nice, have decent MPG but have problem with idle. I have 5 speed stock and if i stop at the light with gear at neutral, the RPM fall down to 1500-1600RPM where stays for about 5-10 sec and then go to to 800RPM where idle nice when hot. When cold it idle maybe too high, at 1000-1200RPM, but RPM does not jump up and down. The car drives otherwise nice without problem, accelerate great.
What could possible cause this problem, map sensor? On www.rockauto.com there is no maf sensor listed for 1991 TBI camaro, so there is no maf sensor? I dont have SES light on, so i didnt try to scan codes. Thanks for help

 

Correct on not having a MAF sensor. I don't believe your MAP sensor to be bad.

For the ECM to do a true idle control the engine coolant temperature needs to be above 85C. At lower coolant temperatures the low side of the engine speed is controlled, but the high side can float. There is only upper limits which are greater then a controlled idle speed.

A lower thermostat or fans wired to always run can cause the idle speed to be too high.

RBob.

 

There is original thermostat at 240?F turning on the single fan, so its not wired to run always. I recently changed the cooling fluid, so now the temperature of the engine stay most of the time on 170F and is not even turning the fan on.
I took a video of injectors, but i think they have a good cone, the only thing im not sure of is there are small streams of gas going down on the side of the TBI unit. So the gas is not sprayed only to the very bottom of TBI unit, but somehow it gets on the side of the wall.
Check the video, but youtube change a quality so its hard to see..

http://uk.youtube.com/watch?v=Wepm3U_ELf4

 

The 170F is too cold. That is 77C, which is below the temperature required for full idle speed control. The stock thermostat is 195F.

Fuel cone: at lower engine speeds the fuel should strike the bores just above the throttle plates. Note how at idle the air flow past the throttle plates shears the fuel into vapor.

RBob.

 

Yep, 160-170 is where the temperature is the most of the time. It could be caused by wrong mixture of cooling fluid or maybe wrong temperature sensor?
With the fuel cone, do you suggest rebuild kit or have the injectors cleaned? If i understood correct, there should not be a fuel on the side of the bore right? Thank for help, i really appreciate it :-)

 

I just wanted to add, that is low for no low-temp stat or fan switch, mine runs around that with the following.

I have a 160 stat and fan switch ( 177 on 166 off ) hypertech.

My idle is 1200 at cold, then warms up and stays around 600-800 and doesn't really surge, is like 600-700 normal for idle on tbi engine? hmm..

There is nothing wrong with this if you ask me, and it's really not too cold, especially for hot summers, mine acutally runs a tad below the line where yours is at, since i added a better radiator, summit aluminum.

When you we're stopped in neutral was it still cold or hot? mine doesnt do that.. of course it's warmed up by then, it only took a sec or 2 to go back down after letting off the gas.

 

I found possible small air leak under my open element, so im waiting for going on some longer trip to see difference.

 

I just returned from 200miles trip and the car seems to work good. I got about 20MPG on highway going 90ish. I read someone is able to get up to 30MPG? Then it got to be for speed of 65-70 MPH? Anyway, im quite happy with result.