Rough idle + high idle

[Christine Suburban]

Howdy y’all! New to the forum! I just picked up this 97 suburban 3 weeks ago. Idled just a little high but overall truck runs pretty ok. Transmission shifts very good. 4x4. I was told it needed a new upper intake as the old one was cracked and the shop wanted $1000. Well I decided this was something I could take on myself. Nope! I replaced it and all new gaskets and seals and it didn’t change a thing! Wasn’t a hard hit I was only $100 more in and a day worth of work. I figured out if I plugged the passenger side pcv going into the air box it would sort of half idle at 700 ish rpm. It was at 1500 cold and 3000 warm. So I bought a lower gasket kit and now water is getting into my oil and it now wants to idle high and then surge. I can post a video if it would help describe. It’s a 99 Chevy Suburban K1500 Z71 with the 5.7 Vortec.

If posting a video will help I can try but I do not see a video posting option? I used all fel pro parts. I was told by an old timer to use fel pro.

Can somebody help me please? I can not find this issue. I’m thinking I need to redo my lower intake gaskets. But I want a second opinion. I’m tired of working on this truck now it’s been a week since I’ve touched it. It’s been non stop raining for the last 4 days and I’m ready to curse the sky.

TIA! -Paul

 

[Schurkey]

I just picked up this 97 suburban 3 weeks ago...

...It’s a 99 Chevy Suburban K1500 Z71 with the 5.7 Vortec.

'97 or '99?

Idled just a little high but overall truck runs pretty ok. I was told it needed a new upper intake... ...I replaced it and all new gaskets and seals and it didn’t change a thing! ...I figured out if I plugged the passenger side pcv going into the air box it would sort of half idle at 700 ish rpm. It was at 1500 cold and 3000 warm.

3000 RPM when warm is not "a little high", it's WAY too high.

Connect a scan tool, find out what the commanded idle speed is, versus the actual idle speed. Does the IAC work?

Verify ALL the sensors and computer outputs while you have the scan tool connected.

So I bought a lower gasket kit and now water is getting into my oil and it now wants to idle high and then surge... ...I used all fel pro parts.

Cylinder head-to-intake manifold gasket surface smooth and flat? Not pitted from corrosion?

Manifold lower section torqued to spec? Manifold not warped?

I’m thinking I need to redo my lower intake gaskets.

Coolant in the oil can be from several sources, but the intake was recent work, and so most-likely cause.

 

[Scooterwrench]

Sounds like the original problem was possibly a bad PCV valve and the shop that quoted you a grand was gonna take you to the cleaners.