350 TBI idle issue

[Tannerm]

Shes getting old and has 154k. When in drive and stoped, it idles around 500rpms and seems sporatically drop in rpms quickly then catch itself. It hasnt died yet, but it jist concerns me.

[SMEGMA STENCH]

Mine does the exact opposite, from time to time. Idles too high. And it dies every once in a while after extended use. Mine turned out to be something to do with the MAP sensor. Still never fixed it though. Have you ran the codes? Sometimes those old chevys store codes in the memory even if the check engine light isn't on. Mine does that.

[Coupe81]

Mine was idling high too and running really cold. It ended up being the thermostat, it was stuck open but now it idles low around 500 too. The idle has a stumble.

[Tannerm]

Hmmm. Ok. Im new to chevys so im just jumpin at every little thing i notice. Ill check into the codes and map sensor. Thanks.

[kingjason]

Spray B-12 around the base gasket of the TBI they are notorious for causing issues. It will stumble if it is leaking. Takes about 10 minutes to change unlike that bastard on my Ford.

[shumpertdavid]

usually if the tb gasket is leaking they will idle higher, not lower. It doesn't have a mass and is affected by vacuum leaks opposite. small vacuum leaks at idle make a map car idle higher. could be the iac or the base idle needing to be set, also check the ignition timing 0 degrees with timing connector disconnected.

[Tannerm]

Well when i put her in park or nuetral, it idles at 700.

[slostang281]

Sounds like an EGR valve issue. I have had the same issue with a 95 GMC and having that problem with my 93 Silverado. The EGR valve sticks open, I just stick my finger in it and jar it a little to close it and runs fine for a while until I get a non- EGR carb intake, pre-87 style heads, cam, chip, and TB adapter.

[Tannerm]

Hmm. Ok. When it is in park or neutral it runs fine. Hell, it seems to run fine whe i got the ac on while in drive. Its weird. I just need to getthis fixed so im not stranded! Where is the egr on these things? This setup is weird with a throttle body on the intake and a single injector in it. Lol im chevy retarded.

[Josh.0]

Lol im chevy retarded.

arnt we all.

[slostang281]

The EGR is on the passenger rear side of the throttle body. It's a flat and round pancake looking thing with a 1/8" vacuum hose attached to the top of it. There will be three or four holes in the bottom of it. You may get lucky and move it up some and the spring inside will push it back down all the way until you're on the highway when it is suppose to open. There is probably carbon build up keeping it stuck open. Mine wouldn't do it all the time but it was the worst when it was cold and depending on how far it was stuck open depended on how bad it idles. Sometimes it would lope like a massive cam and other times it would idle erratically and attempt to die. Another thing to try is spray some starting fluid, brake cleaner or something of that nature on all the vacuum lines with the truck running. Your truck is 16 to 24 years old so the vacuum lines and EGR valve are probably shot.

[Tannerm]

Agreed. Ive done some research online and found that my issue is common with dead EGR valves... They appear to be quite expensive too. Plan is to change oil, do typical "tune up", and clean the throttle body. I can assume its probably pretty gunky.
-side note- I did fail inspection Wednesday during the low speed sniffer on the HC (standard = 137, i failed by 4 points.) and high speed I barely passed. It showed standard HC to be 141 I had 139. I went to Phil's and had a new cat put on. My old (original Phil says) was completely hollow! Kinda nice to know my truck BARELY failed with basically straight exhaust. With the Magnaflow cat, the low speed HC was 9, and high speed HC was 3! Lol I got a 350ci prius. Anyhow, it seems to be a good tight engine with plenty of life left. I just have this nit picky BS to fix.

[kingjason]

Agreed. Ive done some research online and found that my issue is common with dead EGR valves... They appear to be quite expensive too. Plan is to change oil, do typical "tune up", and clean the throttle body. I can assume its probably pretty gunky.
-side note- I did fail inspection Wednesday during the low speed sniffer on the HC (standard = 137, i failed by 4 points.) and high speed I barely passed. It showed standard HC to be 141 I had 139. I went to Phil's and had a new cat put on. My old (original Phil says) was completely hollow! Kinda nice to know my truck BARELY failed with basically straight exhaust. With the Magnaflow cat, the low speed HC was 9, and high speed HC was 3! Lol I got a 350ci prius. Anyhow, it seems to be a good tight engine with plenty of life left. I just have this nit picky BS to fix.

I have seen cars with no cats pass the sniffer. Kinda makes you wonder about how much cats really do on a car if it is running right.

[fordracer2]

EGR valve

x2 on the EGR valve Tanner! Some times you can remove it and clean inside the EGR port on the intake if it is corroded or dirty wich sometimes is the case on high mileage motors. The EGR is easy you can change that out your self no problem. If the idle is rough like it has a cam then it may be the map sensor if is smooth but just low the EGR.How is the stang did you get it straitened out? LMK if you still want me to take a gander at it. Thanx DAVE!

[dumpycapri85]

arnt we all.

It's not us , its the cheveys that are retarded .