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1987 Renix High Idle Issue

Well, I thought I'd update the thread. I got a new IAC. I cold started the Jeep and it started VERY differently. RPM shot up to about 1500 and quickly crept down to around 750. (Beforehand, it would hang around 5-600rpm on a cold start, and go up from there) I let the Jeep run for several minutes to get warm, and the idle stayed consistent around 750ish. I decided to give it a little gas, and as the tachometer fell after a quick rev, it strangely resettled at around 900-1000 RPM. So that's where it's hanging now. Bit of an improvement but still too high. Maybe this gives some new information to someone?
 
Relating to the issues at hand, this morning, I did some more poking around and decided once again to measure the Latch voltage via the diagnostic connector (Pins 3 & 5 of D2). With the car in Run mode, I see 10.7v (Good), with the car started and running, I see 12v. When I shut off the vehicle, the voltage immediately goes to 0. It does not stay around 10-12V for 3 to 5 seconds (I had someone else do the same test I did, and their latch system stays active for 3-5 seconds after the vehicle is shut off). Therefore, my IAC is not 'resetting'? To me, this looks like an ECU problem; it looks like the 'shut-down time delay function' inside of the ECU is not working. I'd like to hear what some of the more experienced members think. Do you think this is an ECU problem? Should I look for another ECU?
 
I wonder if the circuit for always-on power to ECU is broken, so it's only powered when key is on - in that scenario, it wouldn't be able to power the latch relay after the key is off. My '90 FSM says it's B7 on the smaller ECU connector, 16ga red wire.
 
Interesting, So I should probably check and see if there's voltage there? Have my meter leads measuring from Diag Conn 1, Pin 5 to Battery negative? (Pin 5 of Diagnostic Connector 1 is connected to B7 of the ECU) There should always be 12v measuring between said points, correct? Key doesn't need to be in run? Correct me if I'm wrong with anything.

Thank you!!!
 
Checking D1-5 is good move, but I don't think that connects directly to the ECU - D1-5 and the B7 ECU lead are both spliced together (Splice 10-6, MJ/XJ Page 21 in the '90 Electronics FSM) and then go to the starter relay hot lead (10-2, p10) so you could theoretically have 12v on Diag 1-5, but nothing on B7 if the splice failed or the B7 wire was cut somewhere. Not that it's super likely, just saying.
 
mewz99 said:
Checking D1-5 is good move, but I don't think that connects directly to the ECU - D1-5 and the B7 ECU lead are both spliced together (Splice 10-6, MJ/XJ Page 21 in the '90 Electronics FSM) and then go to the starter relay hot lead (10-2, p10) so you could theoretically have 12v on Diag 1-5, but nothing on B7 if the splice failed or the B7 wire was cut somewhere. Not that it's super likely, just saying.
Click to expand...
That's a great point. I see what you're saying, if the splice were bad.. I'll check it anyways and come back with my findings. When I get time later this week, or next week, I'll check for voltage at the ECU connector too.
 
Plans for the day fell though, so I decided to check voltage at B7 on the ECU. There is indeed 12v, so the ECU is seeing Battery + on connector pin B7. Should I get a new ECU?
 
I would think it's worth trying, if you can borrow one...little expensive to buy just to test.
 
mewz99 said:
I would think it's worth trying, if you can borrow one...little expensive to buy just to test.
Click to expand...
I found an 89 ECU for a fair price. Pulled from a running Jeep. It'll be here sometime next week. This morning I completely eliminated C101, took about 3 hours and was very easy to do. No changes in the idle, but still something that would probably have to be done eventually.
 
Got the new ECU in last night and installed it. B+ latch is fixed. Interesting failure. Unfortunately the idle remains the same. I think I might be back to square one, with the idle issue being some sort of a vacuum leak. About the only thing I can think of left, would be worn TB shaft seals, or a compromised intake gasket. I've already tried tightening the intake bolts, and spraying brakleen around the gasket to no avail. Regarding the TB, I'm not even sure if it's worth dumping more money it right now, I guess I'll probably wait till the junkyard has one, and buy that to try. I guess I'm going to have to continue living with it for now, main reason I don't like the issue is because the car slams pretty hard going from park to reverse. Idle literally snaps from 1k to 750.
 
The high idle on my 87 is/is coming back. Looking I noticed the manifold gasket slipping...again.
 
Well, I went through the big process of replacing the intake manifold gasket. Cleaned everything thoroughly, used a felpro gasket, and put a skim of exhaust RTV on each side. Torqued down properly and nicely to spec. Little to no change. Still idling around 1000. Maybe something's wrong with my throttle body?
 
An easy option (although a bit expensive) to eliminate all throttle body questions would be a bored TB from Leigh Performance (Stroked Jeep). You could also check the idle orifice screw on the side of the throttle body and see if it’s been opened. (That’s not the butterfly adjustment, it’s under a cap on the side of the TB)
 
mewz99 said:
An easy option (although a bit expensive) to eliminate all throttle body questions would be a bored TB from Leigh Performance (Stroked Jeep). You could also check the idle orifice screw on the side of the throttle body and see if it’s been opened. (That’s not the butterfly adjustment, it’s under a cap on the side of the TB)
Click to expand...
Regarding the latter.. The idle orifice screw. It's on the driver's side of the TB? Torx? Mine has no cap. Perhaps it's been tampered with?
 
Correct. Yeah, if the cap is missing someone tweaked it at some point.
 
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