Hi Gurus,

All summer, I have been chasing down a sometimes-too-high, sometimes-too-low idle situation on my '92 LT1 A4 coupe. I have been through everything, and I mean EVERYTHING on this car trying to get a normal, steady idle. New plugs, plug wires, removed/cleaned throttle body, new IAC valve, new TPS, new EGR valve and solenoid, new PCV valve, new O2 sensors, rehabbed the injectors (new filter baskets and O-rings), checked for vacuum leaks in every conceivable way, and the list goes on. The idle is actually fairly smooth when it is at normal RPMs, and my BLMs are almost always in the 128 neighborhood, so I truly don't believe that it's a vacuum leak. Often times, when it is idling high (150 - 200 RPMs higher than what the ECM is calling for), I can sometimes just slip the transmission into neutral and the idle will come back down within a few seconds. It's as if the IAC is losing contact with the ECM from time to time. The idle can be either too high or too low, but usually seems to correct itself after a brief period.

I think I have it traced down to either a faulty IAC connector, something in the wiring harness between the IAC and ECM, or something going on in the ECM itself. The IAC connector has seen better days. The clip that locks it onto the tab on the IAC valve is long gone, and one of the little plastic tubes that surrounds the the internal metal terminals is partially cracked away, exposing a bit of the metal terminal. The green rubber seal seems to still be good, as when I remove the connector from the IAC you can feel and hear a bit of suction.

I'd like to replace the IAC connector just to eliminate that possibility, and I know that replacement pigtails are readily available. However, when I look at the 19 year old wire coming out of the harness going to the connector, and see how precious LITTLE there is of it, replacing the pigtail strikes fear into my heart. I also have no clue about the proper way to make such a connection. Crimp-on butt connector? Solder? Heat shrink? I haven't the slightest. Any other things I can check for in the wiring? Continuity or resistance checks?

Tips, tricks and suggestions would be sincerely appreciated.

Thanks!

Ron

Ron I replaced my IAC connector on my 87 L98 in June. I purchased the connector from Rock Auto. Your right I had zero room to splice in new connector. I cut off the old connector and color coded wires and soldered the wires to like color. The replacement connector had approx. 8" of wire which gave me plenty of room with the old connector cut off right at where the wires entered the connector to strip and solder. BTW my old connector was the problem with idling problems. I used a pencil style soldering iron and high lead electronic solder and flux/stay away from acid core solder it will erode your connection over time.
Hope this helps.

Thanks Vetron87. So, for the solder, would the standard 60/40 rosin core solder that you see at Radio Shack work? Also, after you make the solder connection, did you cover or wrap the connection somehow?

Yeah, I would feel a lot better about this job if there was a little more wire from the harness to work with.

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Resin core is fine/they keep changing the composition of solder to remove more lead. 60/40 is great. Coat the twisted wires with flux and burn it in. I used shrink wrap on each wire and wrapped the whole package in electrical tape.
Are you near South Bend??

Hey thanks again! I'm actually closer to Chicago than South Bend. Pretty much right on the Indiana/Illinois border.

Well, I just ordered the part from Rock. I'll have to swing by Radio Shack during the week and pick up the supplies, and hopefully next weekend, she'll be running like a top! Either that, or it'll be a 3,300 lb. paperweight out in the garage! LOL!

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Make sure you put the shrink tube on the wire before you solder.
And make sure the shrink tube is far enough away from the area you're soldering.

Also, if you can find some "Fusion Tape", it works really well. It's like electrical tape except you stretch it before applying it and it bonds itself together creating a waterproof seal.

Yea what Bill said

I just took a closer look at this mess last night, and I think I'll be farming this job out to a pro. The harness is partially buried beneath a couple of coolant lines, there is probably less than two inches of wire coming out of the harness conduit going to the IAC connector, and the wiring is wrapped in electrical tape just about up to the connector itself which makes me think that someone did some surgery in this area in the past. Who knows what I would find in there.

I do believe though, that the connector is in fact the cause of my idle issues. I rigged up a straightened-out paperclip and wrapped it around what is left of the clip that attaches the connector to the IAC and snugged it up as best as I could. In two days of driving including this morning's commute to work, idle has been very steady (knock on wood).

I'm good for now, and the new part is on the way. Just need get ahold of my mechanic to get the replacement installed.

Thanks for all the help everyone!

Ron

Is there not a way to remove the pins from the exsisting connector and just replace the connector? Just wondering since I need to do this to mine eventually.

Yes. It's a weatherpak connector, they changed in 89-ish, but not all at once.

Anyhow, on weatherpak-1 connectors you insert a tool over the pin which presses 2 small barbs in so it can slide out. The tool is basically a ~1/8" thin walled tube. If you don't have that, a broken antenna off a toy rc car works, several sizes to choose from!

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Yea, what CC said.

The tools are cheap, $6.00
http://www.summitracing.com/parts/PCO-0660PT

Also, if you go to replace housings, you have to get one that is keyed the same. A standard Weatherpak 4 position housing may be keyed different from the 4 position on a Corvette.
Keying is where one half of the housing has a slot in the plastic that matches a post sticking up on the mating half. This keying feature can be on any position from 1 to 4 and a housing that has the slot over position 1 won't plug into a housing that has the post on position 4.

I actually found a GM Weather Pack removal tool at my local NAPA store. A bit more expensive than the one at Summit Racing at $10.50, but I guess if you factor in what I would have paid in shipping, I'd probably still be right there.

This thing works like a charm! I was able to pop out the four pins on my old connector with ease. This was nice because I was able to inspect the actual wire/terminal connections closely. Everything looked excellent, so I used the tool again to remove the pigtail leads from the new connector, and just slide the new connector in place on the existing pins and clipped everything back together. Took all of about ten minutes.

Everyone should have one of these in their toolbox. Here's the one I ended up with:

http://www.napaautoparts.com/Search/D ... px?R=NW_725153_0293960869

Bottom line: Did this fix the problem? I've been chasing the same issue for the last 6 months. Nothing seems to make a difference in my car.

I bought the tools from Summit. While on there, I noticed they had the IAC pigtail for $5.95 so I went that route. Just going to use the connector and some Stabilant22 or DeoxIT to on the leads.

Well, unfortunately I'm not entirely sure that it completely fixed the problem. I've been doing some other things to the car concurrently, including working with Jon from FIC on the style of injector that I'm running. In addition to the high/low idle situation, I've been trying to play detective on high BLMs too. Man, I spent the whole summer doing EVERYTHING I could to find a vacuum leak but just couldn't. I had replaced the injectors that my car came with back in March with Bosch IIIs from FIC. For kicks, about a month ago, I pulled out the original injectors that my car came with and discovered that they weren't the factory Multecs, but Lucas disc-style injectors instead. I cleaned them up, and put new filter baskets and o-rings in them, and put them back in my car. My BLMs came back down to the normal range, and though I now had some NEW idle issues going on with the Lucas injectors (mostly just a bit rough and low), I couldn't get the high idle to happen again. I had posted to a thread on this very subject in the C4 tech section on the "other" forum with my findings. Jon saw my post and offered to send me a set of Bosch IIIs that were set to flow about 23 lbs. in exchange for the Bosch IIIs that I had purchased back in March. I put those injectors in last Friday, the same day I installed the new IAC connector. I guess maybe I should have done either one or the other, but I had a busy weekend planned with three car shows and a cruise and wanted to get everything done.

I put close to 200 miles on the car over the weekend, and it did give me one episode of high idle that lasted for maybe a minute or two. The rest of the time, it idled fine. BLMs with the 23 lb. Bosch units are still just a touch lean, at around 135 - 145 on average. Incidentially, it idles WAY smoother with these 23 lb. Bosch IIIs, and the throttle response and power is amazing. I've drove the car to work yesterday and again today, and so far (knock wood) no high idle episodes. I guess I at least eliminated the possibility of a flaky IAC connector causing my problem by changing it.

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That's how it look at too. At least I know that _________ can be ruled out would have needed to be replaced soon anyway.

How do you get the "BLM" readings? Do you use a laptop or some kind of code reader. I keep hearing about people being able to read info from the computer but still don't understand how it is done, can you clue me in, thanks.

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Yes, you need a datalogging software program, such as tunerpro /datamaster, and an OBDI cable to hook from the ALDL cable to your laptop. I bought my cable from moates. I had made my own previously for about $6, but that's not all that great and the premade one is really much nicer.

Here's basic background (lt1 based, principle is the same for l98s)

http://www.corvette-guru.com/modules/ ... ost_id=8735#forumpost8735

Matthew

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What Matthew said, exactly. You can go two ways; either buy a scan tool (that's what I use), or use a laptop computer and the appropriate cable and software. The laptop/cable/software route will usually give you much more in the way of capturing and logging data to go back to and look at. The only reason I use a scan tool is that I found one that would work with my car at an excellent price, but for what I paid for it, I actually could have bought a cable and used my laptop for less money. Either way, the link that Matthew provided, plus other Internet resources, are great ways to learn how the fuel injection systems in our cars work. The factory service manual for your year of car is another. Learning how my car ticks has kind of added another dimension to how I enjoy it.