1994 5.7 idle too low

[Rhonda1994]

Just got my truck back from the shop yesterday!! So happy last person whe looked at her replaced her distributor and ended up too even tightening down the damn thing after replacing it. She has now been retimed but I’m back to the issue before where her idle is too low while hot. Like it’s at like 200-300 rpm low. Her engine has been replaced by me a few years back (still in school for auto tech) I have nobody to tech me this stuff so advice on what to look at or do would be appreciated. I know the last shop tweaked her idle screw but it didn’t seem to do much and he put a used iacv on her. Other than that she runs pretty good. However her wipers only work sometimes lol

 

[docstoy]

I'm new here but will try to help. By your picture you have extended cab 4x4, is it 5.7 (engine) and 4l60e (transmission) ? Do you have a timing light or a scanner ?

 

[Rhonda1994]

She’s already been retimed. But yes I do have a timing light and yes that’s her in the pic, 5.7 tbi. She was out of time bc of the distributor thing but the running “normal now” since they fixed it just the low idle which was the issue before

 

[docstoy]

If you do have a 5.7 automatic it probably has throttle body injection,tweeking idle screw will just change your idle air control counts and if tweeked to much could damage idle air control valve. If above information is true idle speed on scanner should be 550rpm in drive with engine in closed loop, idle air control counts should be 5 to 30. If your looking at tach and its showing less than that could be electrical issue (terminals not making good contact or ground(s) ) . If rpm is actually low , could be timing low, grounds not clean and tight, rich fuel mixture or contaminated oxygen sensor. Factory tachs are for reference only and may not be accurate. Don't just start throwing parts at it if you do have an actual problem as you could make things worse.

 

[Drunkcanuk]

I have seen something about setting the base idle on here before. Something about jumping a wire between two ports in the OBD port.
May be worth the search.

Thread 'Setting TBI base idle (IAC)' https://www.gmt400.com/threads/setting-tbi-base-idle-iac.59449/

 

[DerekTheGreat]

You need to get a scan tool (Snap-On MT2500 is a good choice) and see what it tells you. The gauges & tachs on these aren't known for accuracy. I'd be highly interested in what the IAC counts are. If they're over 0, check the scanner to see what the RPM is. Don't be surprised if what the scanner displays and what the tach indicates differ. Also, how does it sound? If it really was idling too low, your ear will clue you in. Years ago I chased my tail with a big block truck. Tach indicated 1,000 rpm, I thought that was too high. Sounded like it was idling right, but I couldn't look past the tach. Bought a scan tool and found it was actually idling at 800 rpm. Doh.

 

[docstoy]

If you haven't bought a scanner yet, does your timing light have a display on it that shows rpm ? Or do you have a tach/dwell meter ? You can use that to ck rpm if you think it is still accurate . If it's 550 rpm then it's functioning , if you start turning minimum idle rate screw the ecm/pcm is just going to control it by turning screw clockwise (opening up throttle ) you are just going to lower your iac counts, with a scanner you see about 5 to 30 counts, if turned to much it could damage your iac. Ck your rpm and then we will go over how to set idle rate.