Glad to hear it!

Unfortunately guys, I'm still dealing with the issue.

Here's a flip for you, car's been running great the past few days after work. Took it for a drive to several places over a few hours and never saw a single "Check" light. In fact, I've never expereinced it drive so well. No hicups when it's cold, no strange idle, nothing!

However, today I wanted to take it for a Sunday drive and get some lunch.... "Check" light is back but the symptoms have reversed and now it's running terribly. I believe that THIS is finally Limp Home Mode because that's pretty much all it can do... drive around the block, and back up the driveway.

I just finished lifting the car, looked underneath and only found 3 grounds... one was cleaned and re-attached, one was giant and I couldn't reach it if my life depended on it, and another was also out of reach for any tools. I unbolted and cleaned a few around the engine bay but I fear the same results.

I've going to just unhook the battery for a solid 5 minutes and see If I can reset the system because I haven't done that since the new MAF came in.

Fingers crossed.

God help me, this car is killing me, but at least I know I'm close.

 

Check the ground on the water neck.

 

The ground that bolts down with the thermostat?
If so, yes that one's been cleaned.

 

Well?

 

With that ground I would take the bolt out of the thermostat housing and clean it also. They are notorious for corroding all the way down the bolt and right to where the threads make contact with the intake.

Gary

 

Still dealing with the issue. I took a Corvette expert's advice and replaced the coolant temp sender (for guages) as he stated that there might be miscommunication between the sensors, causing a problem on start. Installed the new one and drove it around all weekend and it wasn't going into closed loop (Check Light) ever. He also suggested I either replace the wiring for the MAF as it may be corroded or split somewhere along the line. Looking into that.

This morning, "Check" came right up on start and wouldn't go away even after it warmed up and I restarted it. Also didn't go away when I unhooked the battery for a few minutes, as it did before.

 

That may be good thing, hopefully whatever has been an intermittent fault has become a hard fault. Pull the code and diagnos it, I know its frustrating but hopefully this will be it.
I would look at the coolant senseor for the ecm and see what it shows when the car is warmed up after being driven, this is where live data comes in handy.

Gary

 

wire

 

I'm stripping back all my looms this Saturday to see if I can find the issue. There has to be a single cause there because too many people are dealing with this.

 

Just thought I'd update some of you guys.

I've been able to get the car drivng without the "check" light.
I went back and removed both the coolant temp sensors on the block that I replaced, then replaced those with the original units after I just cleaned the sensor parts off and sprayed down the connectors again with electrical cleaner. I replaced them to begin with because a friend suggested the sensors aren't getting the right sginal and are throwing a code on start-up. However, after I replaced them with new units it made the matter even worst.

I still get the check on cold start, but once I restart the engine when it gets to over 100 degrees for coolant temp, the "check" is gone and it drives normally.

I was able to start it the other night when it was cold, but sitting out in the sun all day, and still no "check" so it's a mystery. I did notice that when I'm starting it cold to get the light, the starter skips a few times then catches and makes a whirling sound. It's a new starter and doesn't make that sound when it's already warm so I don't know how this is causing it to throw a MAF fault code.

Still suspect wiring, but I've been too busy to check everything with my new work schedule and also planning for a new career.

 

I keep saying WIRE because I know it to be a common fault in the early C4 design that brought some attention from the fed dept that regulates and watches things like consumers rights. ALL cars mfg'd and sold here MUST supply parts and have certain basic systems that last 10 yrs. That included the wire harness. The C4 harness was found to be sub-standard at some point. The gauge wire was a bit less than it should have been, the insulation was poor and prone to hardening and cracking when exposed to the common automotive chemicals..petro based products.
My personal experience confirms this. I chased a misfire that would move between cylinders in the rt side...for months I searched and stumbled onto the harness quality accidentally. Grabbed it one day when the eng was running and pulled it out of the way and the eng suddenly smoothed out and ran right for the first time in months. I discovered many cracked wires inside the loom that were cross signaling and grounding out. I had to chop out the entire rt side inj harness and solder in new wire. Have not had a problem since.

Another faulty place is the splices where the mysterious harness grounds originate. This is directly below the wiper motor on the firewall. The splices are simple crimp on metal bands that are NOT covered by anything other than black tape. Thats factory. There are about 5 of these within 2" of each other on the harness trunk line. These are the grounds that drop to the block by the oil filter. The ends are exposed to corrosion, they break, rot and loose the connectivity or conductivity and that changes the performance of the system that depends on resistance values for accuracy.

 

Pull the codes and tell us what you got.

 

Sorry for the late response. Been busy.

I read the codes a few days ago when it was still running well. Then again today after it totally doesn't want to go to open loop anymore... even after I disconnected the battery, start-drive-stop-start-drive-stop a few times, as it did before. Drives a lot better when it warms up, but you can feel it's being held back, unlike how it ran in open-loop yesterday and before.

Codes came back (both times) as 32 and 33.
I know 32 is EGR and 33 is MAF (just like I had before), as I've had before. I know, I know, it's most likely wire related. I can't tinker with it more so I'm going to see a friend at his shop tomorrow for advice... hopefully.

 

Code 33 basically points to wiring. It's either the 12v supply to the MAF, a ground or the 5v reference signal from the ECM. With a voltmeter and noid light you can troubleshoot it. This is not that hard.

 

The shop that has mine has put 30 hours into it at this point, and today he said "I'm sorry but we can't figure it out. It's going to need to go to an electrical shop"

 

I think you and I went through that process a page or two ago.
Results led to the MAF, which I replaced with the Bosch and saw results, but this has moved from intermitent to constant, today.

Unfortunate to see someone else struggling with the same issue.
I know a swap is in my future, but I absolutely don't want to see my baby sit for a year or two while I prep myself mentally and financially.

 

I believe someone mentioned on the first page; looking at the Engine Coolant Temperature Sensor. It's located in the lower front of the Intake Manifold; A bit of a PITA to get to. I had a bad connection there once; it throws everything off, and the car ran horrible; it even gave a code 33; among others.

 

I ended up replacing both the temp sensor and sender, which made the car run absolutely terrible. Once I switched it back last weekend, car ran like a champ everyday until Monday when it threw the same old "check" on start up (33) and wouldn't my go away no matter what I tried.

I could check the voltage on the front sensor. I noticed that there's a good 10-15*F difference between the ECM and gauge sensor reading. For example, I feel the car go into open loop once the coolant temp reaches about 100*F because the idle drops from the 900s to 800s, 700s, etc. HOWEVER, on my gauges, I don't see that the coolant has reached the 100*F mark, basically I see (LOW) while it goes into open loop, and once the gauge reaches 100*F it's already been in open loop for maybe 15 seconds. To me, it seems like the temp sensor and temp sender are about 10-15*F off from each other. I did use this to justify replacing them, but it only made matters much worst. This may or may not still be the problem, but it drove better than ever once I had the originals back in there.

I'm going to stick with wiring... there's no way that something can give such sporadic and intermittent errors and cause such problems that nobody else has... except one other member, who is also following this thread diligently. Unfortunately his wallet is taking a hit, but hopefully his techs find something.

 

That's normal. The coolant temperatures really are about 10 - 15 degrees different between the front of the engine where the ECM CTS is located and the head where the instrument panel CTS is located.

You've got open loop confused with closed loop mode. The car starts in open loop mode and then switches to closed loop mode when the coolant warms up and the O2 sensor starts working. The ECM will also go to open loop mode at WOT.

 

We troubleshot a Code 34 and verified the MAF Burn-Off Module was functioning. I also asked you to check grounds which you say you did. But at this point, you have not checked the reference signal from the ECM. I don't make this stuff up. These procedures are right out of the shop manual.