rb20 idles like s*** when cold

[mott6904]

When ever my rb20 warms up it idles horible. Ive checked for vacuum and boost leaks but havent found any. I have a snap scanner and none of sensors read off at all. Any suggestions in this problem?

[S13 240SX]

a sanp scanner!!! oh god!!!

first of all get a consult hardware and hook up

second of all shouldn't be driving it in the cold anyways.

[mott6904]

I forgot to put the ON after SNAP. I have a snap on scanner and it can do all to the things that consult can do so far. Im not driving it in the cold, im not driving it at all because of this problem.

[240luvr]

Might I ask why you shouldn't be driving it in the cold? It's 10 degrees here right now and I'm about to take my daily driver RB20 to work... Last time I checked colder air compresses into the cylinders better and you'll actually boost better... There's no problem with driving in the cold, Japan gets cold too.

What kind of idle problems are we talking about? Is your idle loping? Do you possibly have it set too low which is causing it to continually try to catch itself? BOV recirculated? If not, is it set too softly? If the BOV is set too softly if will leak at idle and cause a very bad idle, but possibly not on cold start cause it has a cold idle that'll keep the revs up a bit.

[mott6904]

It runs perfect when cold. As it warms up the idle starts to go up and down my tach is off but i think around 550- 900. It seems low and it is drivin me crazy.

[S13 240SX]

do you have a boost gauge hooked up and if so what does it read vac at idle?

[craz4240]

It runs perfect when cold. As it warms up the idle starts to go up and down my tach is off but i think around 550- 900. It seems low and it is drivin me crazy.

The rb20 should idle around 600rpms...sounds perfect to me.It wil idle around 1000 till warm then 600 when warm.Most ppl would kill to have their rb swapped car idle like that out of the box lol.

[mott6904]

When it is cold i think that the vac reading is -18to-20 and then when it warms up it about -12 to -15. Which makes me believe that i have a vaccum leak, but i cant find one. A low idle will also cause this change in vac reading not just a leak. Id rather have mine idle around 800-900. It runs like crap around 600.

[240luvr]

I had similar problems because my idle was set too low. I just bumped it up a bit, now it idles around 750-800 which I was told is perfect. I thought the FSM stated to set it @ 750. But I could be wrong. Either way, bumping my idle up helped. Not positive if that's your problem though.

[mott6904]

I have my idle screw all the way out to try to compensate for the idle but doesnt matter. UPDATE: Whenever it warms up and starts running like crap I took some readings from my scanner. Rpm 600-725, vac -11 to -13, IAC % 10 it doesnt run that good. When i did my wiring i hooked up a wire to the A/C switch so it would kick up the idle when my fans kick on. When i ground this wire out it runs a lot better. Readings with the wire ground Rpm900, vac -14 to -15, IAC % 30. So then i went into functional test in the scanner and increased the IAC % to 40- 45 and it ran perfect. Now my question is the IAC supposed to be a 10% when at idle and is there a way to increase the % on the stock computer?
Modified by mott6904 at 5:55 PM 1/27/2008

[mott6904]

I figured i would go ahead and update on this in case someone else is having the same problem. I found that my tps wire was shorting out to ground. I fixed the wire and now everyhing is fine.

[moso240]

wow u guys got it good...my rb20 runs 2k idle on cold start then 1400 at warm idle...Aem Ems...ever since that upgrade thats been my idle.

[shally2186]

S13 240SX---where r u from in PA?...

mine idles like **** when it gets warm too..like around 500RPM,but i think its something else cause when im cruising around it sometimes wants to staul out when i stop @ a stop sign...my idle was annoying me so thats y i tried the seafoam but that ended up messing sh1t up..need new plugs now and a reset of the ECU..

[mott6904]

What is your tps set at. Once i fixed my wiring i had to adjust my tps to fix this problem. Mine would also idle around that and it would die coming to a stop. I set it to what the service manual said and it didnt work for my car. What i did was warm it up and when it ran like crap i moved to the tps until it ran perfect. I think i had to move it back to about .43 volts i think. hope this helps

[shally2186]

were u refer'n to me too? how do i check wat my tps is set @???

[Bluefire]

Could be tps, could be engine temp sensor, or even aac valve... you have to bust out the fsm and start checking voltages and resistances

-Bluefire

[mott6904]

On the tps you 2 tps connectors, one on the body and one attached to three wires. First check the connector on the body and see if the idle switch is set using the continuity function on a mulitmeter(look up the wiring in a fsm). The other connector you need to probe the positive lead of the multimeter into the middle wire and the black to ground. The fsm said to set it at .50 volts but i had to set it to .43 to get mine to idle right. Just play around with the voltage to see if it runs better,but the idle switch has to be engaged. Like stated above it could also be the ect sensors. To test that unplug the connector and place both multimeter leads on the sensor pins and read the resistance. Check the resistance with the fsm and see if it is within specs. Also did you put some of that seafoam in the iac valve to clean it?

[shally2186]

i just put half in my tank and half in my booster line..i took my IAC out and used brake cleaner on it..