Banshee365

Hey guy's. Past couple of weeks I've been trying to sort out a low idle issue where it idled around 400 and would at some stops because of it. It was hard to start back up. My late 96 model LS has the newer ECU for the stalling service bulletin. After I finally got it started again it raced up to 2500 then back down the 1500 then back up until I shut it off. It was bouncing around. Really weird to me. I've read somewhere that it will cut the fuel at 2500 and reintroduce at 1500 causing the bounce. I removed the IACV and cleaned the valve as much as I could and lubed with a little bit of WD40. It operated as it should with the factory manual diagnostic procedures. When you shut the car off you hear a little clicking noise then a "clunk" like it's fully opening or closing, whatever it's doing. All of this is with the AC off by the way. Trying ot keep things simple. The low idle was still there just a little after the IACV was cleaned.

Shortly after, man did it idle RIGHT where it's supposed to. Right at 650 in or out of gear. Boy was I happy. I figured the IACV started moving a little better after the cleaning and slight lube. I've seen some Gen1 posts where guy's take apart their IACV with 3 screws. On my 96 Gen2 I didn't see where you can disassemble it. Looks like a sealed unit on this generation. I havn't read of anyone taking a gen2 IACV apart.

Now, today, the car started something it's done in the past then went away and started that low idle crap. It's back and forth through a years time with brief points of happiness. Now the car is idling at 1200 out of gear and 800 in gear with the drag of the trans. It's slamming into the gear somewhat because of this. The problem is you can let off the gas and the car will hold 45 mpg on a level road without touching it. It takes off from a stop without touching the gas. There is no sticking in any of the cables, the TPS shows .4 ohm at it's current position with the correct thickness feeler gauge between the stop and arm. The IACV still clicks open or whatever when the car is shut off. I have had an intermitent P0115 coolant temp circuit malfunction. If the car thinks it's really cold all the time it could cause the ECU to cause this idle. I have installed a new OEM temp sensor for the ECU and the problem went away and now is back. I got the CEL and the car didn't change the way it ran. Cleared it and it hasn't come back. I've fiddled with the plug in the ECU that houses the coolant temp sensor wires and nothing is better. I'm going to goto my buddies shop and see if I can borrow his snap-on scanner to see if I can see what the ECU is seeing for a coolant temp and see if that even has anything to do with it since there is no CEL now.

Any idea's guy's? I'm pretty desperate and willing to try anything now. Thought maybe the AC idle up circuit is on all the time but no only would it cause a 1200 rpm idle but when you turn the AC on it goes even higher!! I've searched for intake leaks and don't see any. Any help would be greatly appreciated. Let's roll with this Gen2 idle thread since they seem to be few and far between.

-Kelly

raytseng

seems like you've dug deeper then I have.

but for what it's worth, I had a high idle on a 1990 LS400.
Dumped in a bottle of redline si-i (fuel injector cleaner) on a tankful of chevron supreme. Took a few full throttle pulls on the freeway(i.e. italian tuneup). By the end of the tank, the high idle cleared up.

skperformance

iTrader: (6)

Check the power steering pump idle up valve. As you have done pretty much everything else,
well done.

Banshee365

Can the power steering ACV cause a high idle? I do not get any smoke at startup due to the valve. I have experienced both high and low idle. I usually see the ACV causing a low idle. Right now mind is high. Not exactly sure how the thing works, so I'm wandering if it's even possible for it to cause a high idle condition.

gmacrae

Have you thought about bypassing all forms of factory idle control to see what happens?

You could block off the IAC inlet and block the hoses that supply air to the a/c and PS idle up. Basically make sure that the only inlets into the manifold are the throttle body, crankcase breathers and another hose you can control flow of, it'll need to be roughly 5mm i/d to allow the car to idle well

Drive it like this for a few days to see if it behaves, then hook up the different idle-up bits and IAC one by one to see which one makes it play up?

Just an idea, could help you narrow it down maybe

skperformance

iTrader: (6)

Some where you are getting a vac leak as you tested all the simple lines check the ones that aren't directly open to the atmoshphere like the ps valve .

Banshee365

I've checked all the VAC leaks. Buddies dad's shop has a Snap-On scanner for their troubleshooting. Hooked it up to the car today to see what the ECM was seeing for an ECT. With the car fully warmed up in 95-100 deg Florida weather today in the middle of the afternoon, the ECT displayed between 150-170 degrees. The idle seemed to change as the ECT changed. As the ECT neared 170 the idle dropped below 1,000 and settled in around 800 in park/neutral with AC off. We temped the water inlet housing at 180-185 so the thermostat is working as it should. I thought about replacing it anyways but it seemed to be working fine. Picked up a Stant at Advance Auto but returned it later on due to the fact that it didn't have the jiggle valve.

There isn't an open or short in the ECT circuit at the time. As the day went on the car idled about 800 in neutral and 650 in gear with the AC off. I'm wandering if the coolant system hasn't bled itself properly and there is an air pocket or something near the ECT sensor causing some erroneous readings. I remember the first time the car started idling high was after I did a tune up with plugs, wires, caps, rotors, and a coolant flush/fill. I fillled through the thermostat housing until it stayed to the top of that then torqued down the plug. My draincock was leaking, I replaced the o-ring the other day. Maybe it was leaking before and for some reason some pockets formed due to maybe an issue with the degas bottle. The car has had a pretty erratic idle over the past several weeks. It was low around 400 and would stall out, then perfect for several days, then 1,200. The high idle definetly seems to be because of the ECT circuit. I'm thinking about maybe pulling the thermostat and ECT sensor and putting them in a pot of water with a thermometer with the sensor hooked up to a ohmeter and see if the resistance matches about what it should be at different temp ranges. The sensor is new so I'm thinking maybe the ECM is just acting up. Really don't want to replace that thing. If that's the issue the car would pretty much be totalled if you include that to the fact that it needs a new compressor, evaporator core, expansion valve, dryer, etc... Planning on doing that work myself but still seems around 1200 in parts.

Any input on the cool ECT readings?

gmacrae

it might sound silly, but have you checked for a leak in the big flexi section between the MAF and the throttle?

Banshee365

Just for those to care what the progress is on my horrible running engine issues. It's fixed. My ECM was bad. 1994 and 1996 ECM's are common weakpoints. My car thought it was never warming up the ECT would just up and down causing the car to run really bad. It was constantly dumping fuel in causing the rotten egg smell and flooding out causing next to impossible hot starts. The voltage on the ECT circuit it supposed to be 5V and was well over 8V. Replaced the ECM with a salvaged one that was known to be good and now the car run's like a champ. Idles just a tad low in gear at 600 rpm and 650 out of gear. Starts up perfectly whenever wherever. The ECM can lead to alot of problems and should be looked at when you're coming to a dead end in your diagnosing.

-Kelly

djjazzy

Idle ran high on cold starts on my 1995 LS, took a few minutes (8-10) to come down to normal. If I drove off, the car would run itself for a couple of miles. 147k on the clock. This happened even during the summer, not as lengthy a period however. After seeing someone's post that had the same problem, I disconnected the battery and let it sit for a hour before reconnecting, problem completely solved! This was better than buying a new ECU! Thanks to all for a great forum.

Mark55

Cleaned the throttle body ( removed and cleaned) thought it would clear the high idle but no luck, going to try the battery disconnect tomorrow and see if that will fix the high idle. A month ago my mechanic worked a leaking P/S line and replaced the air filter and the car ran like a dream but the high idle came back which is why I decided to do a throttle body clean out. Any other ideas for high idle out there let me know.