4.8 idle drops too low after pressing in clutch

[cobra30689]

I know this question gets asked AD NAUSEAM throughout this forum, but all the posts I see involve mods.....and mine is bone stock so I'm at a loss lol

2002 4.8 in a Jeep YJ
12212156 calibration from a manual (donor was an auto, reflashed)
Only real modifications to the tune are PE and injector flow rate to allow for returnless fuel system....values copied from a 2004 calibration
Cable driven VSS, speed is pretty accurate but bounces at times

Idle drops down to near 400 rpm (where the stall saver catches it) when pressing in the clutch. Will not stall, but feels sketchy on turns with power steering pump load. Recovers back to 600 quickly.

What should I be looking for? Tune attached, and if it matters....a picture of the intake tube and MAF sensor.

[SiriusC1024]

I'd recommend going over VE and MAF just to be sure. It's not going to be the same, epecially given the MAF location. Want some help?

[blindsquirrel]

You should relocate the MAF. Here's where I put mine, maybe it will give you some ideas.

IMG_20241022_203621860.jpg

[gametech]

Something is wrong with your injector offset table. The numbers don't make sense.

[cobra30689]

I'd recommend going over VE and MAF just to be sure. It's not going to be the same, epecially given the MAF location. Want some help?

Help is always welcome!!

Something is wrong with your injector offset table. The numbers don't make sense.

The offset table was copied and pasted from the 2004 returnless calibration I took the injector flow rate numbers from. Should I change it back?

[cobra30689]

You should relocate the MAF. Here's where I put mine, maybe it will give you some ideas.

Definitely under consideration. My IAT's get quite toasty in the summer.

[Alvin]

I know this question gets asked AD NAUSEAM throughout this forum, but all the posts I see involve mods.....and mine is bone stock so I'm at a loss lol

2002 4.8 in a Jeep YJ
12212156 calibration from a manual (donor was an auto, reflashed)
Only real modifications to the tune are PE and injector flow rate to allow for returnless fuel system....values copied from a 2004 calibration
Cable driven VSS, speed is pretty accurate but bounces at times

Idle drops down to near 400 rpm (where the stall saver catches it) when pressing in the clutch. Will not stall, but feels sketchy on turns with power steering pump load. Recovers back to 600 quickly.

What should I be looking for? Tune attached, and if it matters....a picture of the intake tube and MAF sensor.

1. I'd put the idle a bit higher. Especially for a swap. There was a time manual cars came with a 800 RPM idle and no one thought anything of it.
2. The MAF has changed location and tubing.. so the calibration is going to be far off. Most idle issues are really fueling issues. Make sure the fuel trims are decently close.
3. I've seen a ton of bad IAC's lately. They seem to be aging out. It won't set a code. You can test by using the scanner to drive up and down the IAC positon in bi directional controls. Make sure when you go to 0 the idle dips or dies, and go high the idle raises.


Lets see a log with IAC count, TPS voltage and %, STIT and LTIT as a start.

[cobra30689]

Lets see a log with IAC count, TPS voltage and %, STIT and LTIT as a start.

I've loaded the laptop with the proper channels, and I'll get you a log on my way to work tomorrow morning.

[gametech]

[QUOTE=



The offset table was copied and pasted from the 2004 returnless calibration I took the injector flow rate numbers from. Should I change it back?[/QUOTE]

My bad. I guess I just never paid attention to 2004 non-return offset tables. It seems bizarre to me that the numbers dip down lower in the middle of the table than the numbers to the left or right. However, I just looked over 5 stock tunes from various places that look identical.

[blindsquirrel]

The later returnless trucks with those same injectors do have a quite different Short Pulse Adder table, though.

[cobra30689]

I'm pretty sure I added all the channels y'all might need. Let me know what you think. There are definitely a couple of drops below 600 in the log. IAC counts seem to be good?

[cobra30689]

The later returnless trucks with those same injectors do have a quite different Short Pulse Adder table, though.

What effect does that table have, and should I change it?

[Alvin]

I've loaded the laptop with the proper channels, and I'll get you a log on my way to work tomorrow morning.

Did you read what else I said?

IAC counts are low in this log. The other things I said still apply.

[cobra30689]

Did you read what else I said?

IAC counts are low in this log. The other things I said still apply.

I did! When I got home I raised the idle to 650. I'll take it out later and see if that helped. As far as the IAC counts.....what am I looking for? By what I see on the log the counts mirror each other closely....if I had a bad valve, wouldn't the actual IAC count be quite a bit off the commanded count? The valve responds in a proper manner when I use the bidirectional controls. Fuel trims seem to stay within the accepted +/- 10% range, but it looks like a MAF calibration is in order.

[edcmat-l1]

The IAC counts are too low indicating the throttle blade is open too far or it's getting air from somewhere. The IAC counts should be 40-60 at operating temp. If you bump the desired idle up to 750-800 and don't change anything else your IAC counts will probably be right where you want them.

You need to add timing advance to the pid list. Also throttle cracker and throttle follower.

[cobra30689]

Sorry to take so long to reply with a log. Raised idle to 650, but still drops into the 500's. Added the requested PID's as well.

[ns158sl]

what cal is that car from? Id enable rolling idle for a test.

[cobra30689]

what cal is that car from? Id enable rolling idle for a test.

2002 Silverado 4.8, manual trans.

I've asked this question before but the answers I got were a little fuzzy.....does the clutch switch come into play for anything? I don't have one, nor do I have a way of installing one (older Jeep YJ).

[cobra30689]

The IAC counts are too low indicating the throttle blade is open too far or it's getting air from somewhere. The IAC counts should be 40-60 at operating temp. If you bump the desired idle up to 750-800 and don't change anything else your IAC counts will probably be right where you want them.

I'll try bumping the idle up further. But that leaves a question, why would I have to on a completely stock, unmodified engine? Or is it the difference in my air intake?