RENIX ECU Idle differences

[mythreesons]

I have spent some time reading through search results but can't seem to find all of the answer to this question.

 

If you have a 88 4.0 that was originally an auto (auto ECU) then changed to a manual (first time to a Pukey then to a AX-15) BUT the ECU was never changed...... the end result will be that the engine runs fine but with a higher idle, but by how much?

 

I have to get under the dash tomorrow anyway and will check part numbers on the ECU that is installed, but I cannot find the reason for the higher than normal idle on this truck. I have been working on the vacuum lines, checked and replaced the TPS, will be checking the MAP sensor in the morning, even checking the intake bolts. It's getting better every time, but still too high for my liking. Currently at cold start-up it runs about 800 RPMs then creeps up to 1250-1500 as it reaches operating temp. It varies in that 1250-1500 range a little like it's hunting for something but I don't know what.

 

Anybody got any other idea's to check?

[Pete M]

how many of the vacuum lines have you replaced so far? is it 4wd? do those vacuum lines still exist?

[jpdriver1]

thx pete --- been trying work an idle down from 950 ----- duh forgot about the 4WD lines

[mythreesons]

how many of the vacuum lines have you replaced so far? is it 4wd? do those vacuum lines still exist?

 

 

I'm working on them. (Graveyard hours at work doesn't leave a lot of time before much needed beauty rest.) The vacuum lines going downstairs are not even connected. (Actually, now that I think harder about it, I think that the front axle has been replaced sometime previous and there is no CAD on it.) I am still trying to figure how to hook up the new "football". The truck doesn't have one..... Just the big vacuum line that used to go to the football is connected to a small line that goes to the firewall for the heater control valve and the blend door. I haven't pulled the dash open yet to check for leaks.

 

I have been all over the engine compartment with the propane bottle and now have no change in the idle from that test. But the idle is still high. I have to get into the dash to straighten out some wiring so I'll check the vacuum lines then. Additionally, I did poke my head under the panel to see what part the ECU is..... it has a Re-manufactured sticker on it without part numbers written on it. Yea! :wall: So I guess while I have things open under there, I look a little closer at the ECU to identify.

 

Oh..... the fun of older vehicles. They are really like mystery novels where we get to write the endings.

[Pete M]

have you cleaned the throttle body out? specifically the IAC?

[deziped]

Pete, I was about to mention the IAC. Had a slight problem with high idle on mine over the weekend. Turned out to be crud in IAC as after removing it and squirting it down with carb cleaner (and in the hole in TB) it cleared it up. M2C

[Fezzik]

IT's funny, my Mj has started to idle at ~2500 sometimes on start up, I was thinking that, does someone have a picture of where the IAC is on a Renix 4.0? Oh, and cleaning it something a simple backyard mechanic can do?

 

TIA

Karl