While I was away at school my dad had the muffler replaced on my ummm k1500 3rd gen, because it had a couple rather large leaks. Also took it in for a tune up at our friends shop, and it seems to be running a lot better now. It doesnt stutter like before, doesnt lose power momentarily up hills, and feels more solid throughout the powerband. However, the idle still seems to be way high. Right when i start it, it shoots to like 1400rpm, then when i shift into drive/reverse/etc it drops to about 900 or 1000. Maybe its just been too long away at school, but i remember it being more like 600-800 at idle. The thing MOVES while idling now, and it is not a light vehicle. If itake my foot off the brake in drive and let her idle forward i will get going pretty fast pretty quick. Problem or just more powerful after tune-up and exhaust leak fix?

 

My 305 idles at about 1500 when I first start it up. After about 45sec. it starts to drop to 1000. After about 1.5 min. it stays at 600 RPM. I think the engine is trying to warm up when started cold. You say that your motor idles at 1000 after reaching normal operating temp? I am new to THIRD GEN, but here is my idea. Did your car have a heat riser orginaly? If so, did it get taken out when your dad put in a new exaust? Or maby its your coolant temp sensor ?(not the temp gage) Just an idea, Im not shure.

 

Also, idle is computer controled on TBI's . There is an adjust screw, but it is covered up, and NOT recomended to adjust.

 

ok well figured it out. apparently the fast idle controll for cold startup was faulty on my engine this whole time. Now that things are fixed, the fast idle is higher because it was supposed to be all along. I knew they had a cold startup high idle, just didnt realize it was that intense. Now that ive driven it for a day, i notice it calms down pretty quic. And my dad told me

 

check for a vacuum leak at the tbi gasket. this is a common problem with tbi engines.....will cause idle to be too high.
computer does control idle with iac valve but it can only lower it so much. if you had a scan tool you could watch the iac counts to see if it is working. i would start by checking the tbi gasket thou

 

Hey, I having the same problem with my tbi engine. The idle shoots up to 1400ish and only calms down to 1000 rpms in park and 900 in gear. When you put in gear its wants to take off really quick unless you mash the brakes. I checked all the hoses and replaced the tbi base gasket and still idles higher than I like. I looked at the set screw and it has a soild plug not cap like my tpi. Can the idle be adjusted at all? No check engine lights and runs fine just dont like the idle. It makes winter driving on slick roads very interesting. I have to put it in neutral to keep from sliding through intersections. Are all tbi setups pretty much the same from the 305 to 454. My engine is a 454 tbi chevy.

 

Pretty sure tbi setups are pretty much the same....There is a adjustment screw that can be access if a plug is knocked out. I had an Astro van that I adjusted the idle that way.....It had a weird idling problem too. The iac valve was reading zero counts which means it had lower the idle as far as it could. if yours runs fine otherwise I would remove the plug and lower the idle....

 

You can do that, when I set the idle via the screw (which I have had to do after cam swaps), I unplug the IAC, and then then set the idle with the IAC in its park potions, I try to set it in the 450'ish RPM range with the IAC in park, that seems to give the IAC all the correction range it needs.

 

I have a camaro 1992 z28 tpi
and it idles high when i start it, the idle is 3000 then it dopes
to 1500 sometimes, but most of the time it stays at 2000-3000 rpms. SO i ran a computer on it and because the check engine light kept going on, but would never stay on.It might turn on for about 30 seconds and turn back off,or sometime it would stay on for 15 minutes then cut back off.While back to the subject the computer said it was the tps sensor so i changed it but same problem but the idle would now say at 1500-2000 rpms
i was reading a couple of threads and it said that when your engine is could it should idle at 1400-1500 but once it heats up it should drop to 750-800
"nidyanazo"er...in the morning (EVERY day) when i start 'er up, i get that 1400-1500rpm
idle for 6-8 minutes or so, then it slowley drops down to the norm 750-800rpm.
Is this normal or a sign of some mis-adjustment?

i had a mechanic adjust my idle and some problem it also hestates
alot i change the fuel filter and did alot of them things you recommeded, can somebody please help me

 

you might check the electical connectors on the IAC, mine came uplugged once, and the thing idled crazy fast, just like you are describing.

 

Truck just got out of our friends shop again, the trans was jerking around and the idle was still high so they took a look. Turns out the TPS was going bad and basically thought I had my foot slightly on the gas even at idle. Dad said it runs great again, I'll check next weekend when I go home.