After replacing gaskets and valve stem seals, I had timed the engine to 10* BTDC while cold and then as it warmed up I noticed that it was a very inconsistent idle. It would hunt as low as 550 to up to 750-800 and very erratic. Once warmed up, I adjusted it back to 6* BTDC and the idling smoothed out and hunted between 550 and 650

What I'm curious about is that I've read that 10* is better but doesn't seem to be better from an idle perspective with my particular set up.

Recently I've done the following:

• Replaced CTS, TPS, O2
  • Set TPS to .525
• Replaced intake gaskets including top plate
• Replaced TBI gaskets

I also got an ALDL cable and used WinALDL to view the raw date (and subsequently have it graphed as well). I could see that sensors appear to be reading correctly. The only thing that seemed to be abnormal was the coolant temperature was not going past 183 degrees but what was odd was that when I turned off the engine, the coolant temp rose to 190 according to WinALDL. I have a sneaky feeling that the thermostat may have shifted again some how. When I reinstalled it with a new gasket, I verified that it was still in the correct position by looking down the thermostat housing before putting the hose on. I do have two small holes on the thermostat to help minimize air in the system, could those holes be enough to prevent the system from getting to temp? I'm assuming that it could be preventing it from getting to operating temp and further preventing it from going to closed loop. For additional context, after running for 50 minutes in my garage (couldn't drive it last night) the temperature peaked at 183 according to WinALDL.

Other than that, what are some other things I should be looking at with WinALDL?

 

If you have a 180 degree thermostat. Sounds perfectly normal. Rise in temp after shut down. Perfectly normal.
hunting idle? Not perfectly normal. Vacuum guage bounce? Vacuum leak? All valves adjusted properly?

 

Did you disconnect the ECM from the distributor before adjusting your timing?

 

I don't have experience with the winALDL but if it works similar to a scanner, open/closed loop is should be indicated on the laptop in the data stream. Keep in mind that it's normal for some cars to go back open loop at idle. However I doubt that your idle issue. Try unplugging both IAC motors and see if the hunting stops. This will distinguish whether it's a air problem or fuel problem. I've noticed that you haven't replaced the MAP sensor. I'm not one to fire the parts cannon, but replacing the MAP sensor would be a good idea. I would like to see a video of the winALDL with the full data stream with audio of the car running.

 

One more thing, are you reading MPH on the winALDL while driving?

 

I did. Made sure the EST wire was disconnected during timing.

According to the readings, at 550 RPM the MAP sensor is reading 43 kpa when RPMs would go up to 675 the MAP was dropping down to 35. Of course I'll need to check potential vacuum leak, probably do another propane test. Thermostat is a 195. When I initially adjusted the valves, I had them tightened to one full turn after zero lash. After running for a bit and seeing more than usual exhaust I backed them off to one-half turn after zero lash.

 

I'll work to get a recording along with live stream data. I'll also give it a test with unplugging the IAC motors, should I do that once warmed up?

I also have not yet gone driving to get data that way yet. Definitely on my list of things to do though. I had not yet done that as I was more so excited that I got the scan tool and wanted to try it out. Wasn't anticipating on turning into a troubleshooting session until I realized that the idling was fluctuating so much. My data right now is a bit skewed since I didn't have timing set correctly when I initially started capturing the data. The last 3-4 minutes is all I have so I'm trying to read too much into that data. I'm looking to getting a better data set tomorrow when I'm able to fire it back up again.

 

Forgot propane for leak detection, get a eBay smoke machine. I have the same one and it's excellent for home use.

 

Have you looked around on the C4 section of this Forum? There are several people who use the OBD1 Scanning using an adapter made by company. 1320electronics.com or something like that. I bought the module that allows me to see and save data from the OBD1 system. It also does awesome graphing of several sensors at the same time. They sell a variety of great devices allowing up to more closely see what our Corvettes are doing.
Since they are popular there on the C4 forum then you should find people that can explain how they are used better. I would start at the company's website and see just what 1320electronics can do you and your Corvette. I have a 1988 C4 as well as my C3 so I keep my options open with OBD1.

 

I had a very similar issue with my crossfire and I never could get it to idle right. The problem was that the EGR valve was stuck open. Also, have you checked the balance of the TBI's after you did all that work?

 

I'll look into that, was just going with propane as it is what I have available so far.

I also tested unplugging the IAC motors after the engine was warm. When restarting idle was about 1900 RPMs. I did not test by unplugging while running.

From what limited testing I have done, EGR seems to be okay. Not ruling it out of course. The EGR is less than 6 months old. The testing that I have done so far has been using a vacuum pump at the EGR directly and testing operation when applying a vacuum, and running the engine with the EGR disconnected and plugging the vacuum ports. I did notice today that the vacuum line from the boot of the solenoid to the EGR valve is loose so I have a feeling there may be a vacuum leak there to which I am going to work on plugging. I also have not done any balancing.

I took the car for a drive today with the ALDL cable connected and captured live data and have a few take-aways/items I'd like to see if anyone can shed some light on:

• RPMs appeared to be around 100 RPMs off. For example, the Dash would show idle at around 700 RPM but the live data was showing 600 RPM. I'm not sure which one to believe but am leaning more towards WinALDL as I have seen that the circuit board can fail. Not putting my eggs all in that basket but that's what I'm leaning towards.
• Coolant Temp still reading at around 184. Going to look at pulling the thermostat housing to verify it's in position and re-seat if needed. Though, I am wondering if this could be off by a few degrees. Going to look to see if I can verify accurate readings with a multi meter soon.
• Speed seems to be accurate. I recall driving around 50 MPH and matched that up to the data.

 

If you like, give me a call and we can talk about this issue. I think I can help you. PM me and I'll give you my number. Also, do you have a 82 GM service manual?

 

You need to do that test with the car warm and running at idle. It's a quick way to rule out anything with the IAC circuit. It will not throw a code or do any harm. The winALDL is the correct RPMs.

 

That coolant temperature looks normal to me.

Take Buccaneer up on his offer! He will get you on the right track for sure.

 

Maybe it's now solved by Buccaneer.

I was just curious about something since you say you haven't done the balancing yet.

With both the IACs disconnected and engine up to temp, have you ever adjusted the minimum air adjustment screw to get the 475 RPM (I used 500) in drive before doing the balancing? The minimum air adjustment screw is located on the drivers side throttle body behind the throttle linkage. Its the stop screw for the throttle at idle, similar to an idle speed screw on a carb. I'm wondering if that minimum air adjustment screw setting is off. Did you do something like this:

• With engine off and warm, disconnect both IACs
• Plug the IAC ports with some pool noodle foam or similar cut in a wedge and pushed in so air can't get into the intake manifold through the port.
• Start engine again and adjust the minimum air adjustment screw to get the 475 RPM in drive
• At this point, this is where you'd do the balancing. If you didn't want to do the balancing, maybe you could skip this step as a test.
• After shutting the engine off, now reset the TPS voltage again to the 0.525V with the new throttle stop position.
• Remove foam plugs
• Plug back IACs and reset with speed.

 

To add, I think that gives the IACs a proper baseline to work from.

 

I can confirm that I did not do any of that. But will look to do that in the coming days.

However, after doing some testing earlier, I had disconnected the IAC's after warm and plugged them back in. Now, when I start the engine it idles very very poorly. I looked in where the IAC pintles extend and they both are fully extended. I also hear a clicking sound while the engine was running. I assume that is not ideal. That said, how do I reset the IAC's to fully retract? Is it as simple as disconnecting the battery for a period of time and then try again or is there something else?

 

The IAC resets after driving the car a few miles and achieving converter lockup. Did you unplug the IAC while the car was run and did the idle stabilize?

 

I don't even think you need converter lock up. The factory service manual on page 6C1-4 says the IACs reset with speed over 30mph or if you have cruise control, you can disconnect the upper speedo cable to the dash and spin it with a drill to obtain an over 30 mph reading with the key on.

• Is the minimum air adjustment screw set so low that the butterflies are almost totally closed with the foot off the pedal? This would mean that not enough air is going around the butterflies at idle and would likely make the IACs try to drive wide open to the limit, in an attempt to allow enough air for an idle.
• Or less likely, did the wiring to the IACs get messed with and maybe polarity is backwards driving them open instead of closed? You mentioned before there was some wiring issues with the temperature sender.
• You said the Speedo was accurate reading the ALDL so it should have reset if you were over 30.

 

Nonetheless, it wouldn't surprise me if the Minimum Air Adjustment Screw was messed with by someone to try and compensate for those vacuum leaks you found on the manifold by closing the butterflies more in their idle position.