88-c4 idle issue

[my88]

When I cold start the engine it idles to 1100 rpm and takes about 4 minutes to idle down to 700. When starting warm, it idles to 1100 and then takes about 1.5 minutes or longer to idle down to 700. Is there a way to shorten the idle down time? (New IAC and no known vacuum leaks)
Thanks

[c4c5specialist]

HI there,

When a new IAC is installed, it must have a minimum idle air rate set done so the ECM knows where to idle the engine.

If this process isnt done, than your engine can experience this condition.

The procedure is long and is in the factory service manual.

It does require a couple of tools to do it.

Allthebest, c4c5

[my88]

When installed I did the adjustment

[c4c5specialist]

HI there,
There is then either a vacuum leak or the ECM is not compensating to engine speed.

Either way, you will need your IAC counts to validate this.

You are looking for 30 counts or close to that. As you view it on a scan tool.

Allthebest, c4c56

[my88]

Will try again in the morning
Thanks

[lovehatec4]

Originally Posted by my88

When installed I did the adjustment

When you did the adjusment properly on the IAC,did you adjust it at normal operating temp (190 or so)? also readjust your tps voltage to .54 volts at wam idle? Here's the deal, when you adjust the IAC..you turn the set screw, and even a quarter turn will change the TPS voltage. Lets say its now .58,,this could and will probably make your vette idle faster. The .54 volts at warm idle is very important on C4s. When I changed and adjusted my IAC, it idled really high until I got the tps adjusment right dead on perfect. I hope this helps... let us know.

[my88]

TPS showed .51 volts......set to .54......this actually made it worse,it now takes longer to idle down...????? I checked it with a scanner and a multimeter

[lovehatec4]

[QUOTE=my88;23773]TPS showed .51 volts......set to .54......this actually made it worse,it now takes longer to idle down...????? I checked it with a scanner and a multimeter[
/QUOTE/
Is your c4 an automatic? If it is then start over adjusting the IAC properly.First, Get the c4 to @ 190 (normal temp) then turn the key off and insert a jumper from the A port to the B port on the diagnostic connector under the dash. Then turn the key on and wait 30 seconds.This will reset the IAC to the retracted position. After 30 seconds and with ignition still on, diconnect the IAC connector and the distributor EST wire. With the key still on, start the c4. It will idle realy low and might try to stall. prevent this by feathering the throttle until it idles on its own. Now remove the jumper wire from the diagnostic port. Then with the parking brake on and wheels chocked,put vehicle in drive and set the idle at 400-450 rpms. If your c4 is a stickshift then adjust idle speed to 500- 550 rpms in nuetral. Use a proper tachometer, not the one on the dash. The dash tach isnt accurate enough. After setting the rpms this way, Turn the ignition off and reconnect the IAC and the distributor EST connector. Then disconect the negative cable from the battary for five minutes to reset the light on the dash.
After and only after this has been done correctly should you set the TPS to .54 volts. Also before doing any of the above, check your timing with the EST connector disconected. Should be 6 degrees BTDC.
After you drive it about 15 minutes, your idle in drive with a/c and heater off should be @ 625 rpms (auto trans) and @700 rpms If you calibrated for standard trans.
I hope all will forgive the length of this post,Just trying to help...let us know.

[my88]

Thanks...MUCH BETTER....In summary,the idle was spot on,the changes I made were:
Timing 10 to 6 BTC and Iac .51 to .54v
Thanks again

[lovehatec4]

Originally Posted by my88

Thanks...MUCH BETTER....In summary,the idle was spot on,the changes I made were:
Timing 10 to 6 BTC and Iac .51 to .54v
Thanks again

Your welcome. I glad it worked out.