1990 c1500 5.7tbi Rough idle when warmed up Help Wanted!

[Sabinoerc]

It looks like the Bosch can be put into ”field service mode” which is shorting out pins A-B but doesn’t have option for 10k/ALDL mode which is the 10k between A-B. So I’d guess the 10k resistor is in the cable between unit and ALDL connector. I could see the bosch unit having capability to short something or not - and the default resistance between pins is in the cable. You could verify this by checking resistance in cable unpugged from test unit and car. If so, you may be able to figure out how to change or make your own cable without the resister.

you mentioned fuel pressure is 11psi “before” fuel filter. If “before” means between fuel pump and filter, I’d check again between filter and TBI.

 

[hbryant123]

I'm gonna check fuel pressure up at the throttle body, it was 11 psi before the filter , filter was changed about 3 years ago, could be clogged . Fuel pump was replaced about 3 or 4 years ago, I used a Delhi pump.

 

[hbryant123]

W.r.t. the ”10k or ALDL mode”. https://www.thirdgen.org/forums/diy-prom/247135-idles-faster-when-aldl.html

when running in that mode ECM doing more than just changing idle speed. Supposedly for some sort of end of line mfg test or fast diagnosis of certain problems - I don’t know.

I‘d think that would be programable, maybe setting options on interface is not specifically saying ”10k” mode, using different name for the function?

I played with the scanner more last night, I read a more detailed manual on bosches website, it does have a field service mode that mentioned crossing those two pins, it just caused the ses light to blink, sorta like when we read the codes with the paper clip.

 

[hbryant123]

Update, I did check the fuel pressure right at the throttle body, it is 11psi!

 

[Supercharged111]

Update, I did check the fuel pressure right at the throttle body, it is 11psi!

That's a little low, but shouldn't cause it to run like total poo.

 

[hbryant123]

That's a little low, but shouldn't cause it to run like total poo.

Yea, the part that stumps me is it runs great any other time than at idle!

 

[Schurkey]

Last time my truck had a crappy idle, the intake gaskets were deformed. Caused an air leak into the fuel/air mix affecting two cylinders.

You must be registered for see images attach

 

[hbryant123]

Last time my truck had a crappy idle, the intake gaskets were deformed. Caused an air leak into the fuel/air mix affecting two cylinders.

You must be registered for see images attach

With the age and mileage (185,000) I'm considering replacing them and cleaning the throttle body as maintenance!

 

[hbryant123]

Update, Im still battling this rough idle issue, I have returned the bosch 1300 scanner, I ended buying a moates cable and downloading winaldl so we can view live data at idle without any strange issues!

Since I have the proper setup to view data what do I need to look for, I dont have a good running truck to compare to is my issue now. Does anyone have a good reference on what the readings should be?

 

[PlayingWithTBI]

I ended buying a moates cable and downloading winaldl so we can view live data at idle without any strange issues!

I'm curious, why WinALDL and not TunerPro RT?