When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Really Stumped At This Problem. Could Sure Use Some Help!
I have a 1996 LT1, bone stock. Runs and drives great. But I am having a hot start problem. When cold it fires right up. It'll also fire up right away when hot if I start it within a few minutes of turning it off. But if I leave it for 10 minutes or more, the motor cranks as though it's flooded. It'll restart every time, but it takes a few turns of the key and when it catches it's not a "smooth" start. In an effort to address the problem, I have replaced the following:
Fuel filter
Fuel Pressure Regulator
Idle Air Control valve
New 24lb. Injectors
Temp Sending Unit (the one that goes to the computer)
The only thing I haven't replaced is the fuel pump, although I have a new one. I'm not sure that would help because I have good pressure and the car starts fine under all other conditions. This problem only surfaces when the motor is at temp and has been sitting for a bit. I'm really beating my head agains the wall with this one. So before I start to bleed, does anyone have any suggestions as to what might be causing this problem?
Thanks in advance.
Last edited by Rogue One; Mar 21, 2026 at 10:48 AM.
Is there visible black smoke after the 'difficult' hot restart? (With new injectors and pressure regulator, there shouldn't be, unless you have a bad replacement part.)
Being a 96 OBD II, the onboard diagnostics don't query engine codes, so you need a cheapo code reader. You should check for codes, if any found note them and clear them. If any of the same reappear after the next incident, I'd be looking at those diagnostics in the FSM.
After a heat-soak, ie when you expect it will be difficult to restart, check the voltage between the blue and black wires on the TPS with the key in RUN. (Use paperclips to back-probe from the wire side.) Voltage should be in the .54-ish range. If in the 2.xx or higher, the system may be going into clear-flood. Although with a 96 Automatic, if the TPS is acting up, this should also show in shift-point behavior. Still worth checking.
Started heat soak?? If cranks after it cools off, might be it ..
Yes, I'm thinking this condition is a result of the heat soak.
Originally Posted by IHBD
Is there visible black smoke after the 'difficult' hot restart? (With new injectors and pressure regulator, there shouldn't be, unless you have a bad replacement part.)
Being a 96 OBD II, the onboard diagnostics don't query engine codes, so you need a cheapo code reader. You should check for codes, if any found note them and clear them. If any of the same reappear after the next incident, I'd be looking at those diagnostics in the FSM.
After a heat-soak, ie when you expect it will be difficult to restart, check the voltage between the blue and black wires on the TPS with the key in RUN. (Use paperclips to back-probe from the wire side.) Voltage should be in the .54-ish range. If in the 2.xx or higher, the system may be going into clear-flood. Although with a 96 Automatic, if the TPS is acting up, this should also show in shift-point behavior. Still worth checking.
No smoke at all. Thing starts clean. Thanks for the tip...I found a YouTube video that shows exactly how to do it. I also saw a vid on how to do the flood clear function. I never knew about this. Will get on it and kick myself...HARD...if this was just an adjustment issue
Now...if only my multimeter's batteries are good..........
Originally Posted by Ratboy
Maybe its ignition? Those opti-sparks are trouble when they get old.
I suppose that's possible, but the car runs great even after a hard start. I sure hope it isn't that.
So I went to back-probe the Throttle Position Sensor by sticking paperclips into the connector from the rear side. Imagine my (lack of) surprise when I saw GM changed the connector to a design where you can't stick a wire in and the inside are small pins that you can't attach a wire to. Oh...and also...GM now attaches the sensor with three Torx cap screws instead of two. Kinda makes it hard to pivot the damn thing. Anyone have any ideas as to how I can get a reading on this?
Anyone have any ideas as to I can get a reading on this?
I didn't have much difficulty. I verified contact by checking each 'pin' to ground with my VOM. Picture taken 3 days ago and posted in "how do I wake up my ?" thread.
I didn't have much difficulty. I verified contact by checking each 'pin' to ground with my VOM. Picture taken 3 days ago and posted in "how do I wake up my ?" thread.
Thanks for that pic. I didn't think it could be done. If I'm seeing correctly, you went with the blue and black wire. Also it looks as though there are 3 Torx screws. The YouTube video I watched only had two and he turned the body of the TPS to adjust the voltage. Do you loosen/remove all three to adjust?
Originally Posted by Whaleman
When I had a hot start issue on my 96 it turned out to be the fuel pump. I tested with a loaner gauge from Autozone. Dan
I have one in the box ready to go just in case.
Originally Posted by Steve Swan
@Rogue One Following with solid interest. My '96 LT4 has the symptoms you describe. Please post what you find that eliminates the hot start issue.
If I'm seeing correctly, you went with the blue and black wire.
No. I am probing the gray and blue wire. For this picture I was intentionally forcing the TPS signal (blue wire) high by jumping it to the 5.0V reference source. (gray wire). To check TPS signal voltage at closed throttle you meausre between the blue wire and black wire. Ie between the TPS signal and ground.\
Also it looks as though there are 3 Torx screws. The YouTube video I watched only had two and he turned the body of the TPS to adjust the voltage. Do you loosen/remove all three to adjust?
There's only two screws. Looking at my pic (I didn't go out and lift the hood) it appears that the screws are in round holes. There would be no ability to "adjust" by rotation. I also have an intake assembly for a V6 CPI that has the same TPS and its holes are slots; ie it can be rotated to adjust.
Reading the FSM reveals that the ECM will accept a value between .03 and .09 Volts. Upon power-up, the ECM reads the TPS voltage and uses it for the remainder of that key cycle as the closed-throttle value. There IS however a 'learn procedure' for the ABS/TCS zero-throttle position that requires the use of a TECH-1 with BRAKE module to calibrate the 0-throttle TPS for the ABS/TCS.
Again. Because the TPS is used for shift-timing for the 4L60e (94-96), if TPS is erratic or really wrong, you would experience shifting 'problems' with your electron transmission.
One more thing: Some systems have "clear flood" and some don't. My 92 LT1 does not have "clear flood". With the jumper pictured the ECM thought my foot was on the floor, but it fired right up. So you may be chasing a ghost if your 96 does not have clear flood. It may not. Run the experiment I did: Jumper gray to blue and see if it starts. If = yes, it does not have clear flood and TPS has nothing to do with your hot restart difficulty.
@IHBD Thanks for the information. Sorry to be MIA..but I had to decouple from Corvette world for a bit as real life took over. I will still go out and check the TPS in short order. I did want to mention that I saw video showing how to adjust the TPS sensor. Now, I know that the car in this video has an L98 engine, and the connector is different, but he is saying not to allow wires (or, leads connecting to the wires) to touch. He also shows how he turns the sensor to adjust the voltage. Not a bad video if you have a moment to check it out.
Heat soak affected my 1st ICM in warmer months. It cools down pretty quick once coolant starts passing thru the cyl head behind it again and will present as many other things. Tricky to diagnose. I'd start with verifying if fuel psi is bleeding off after sitting with a pressure guage. That's fuelpump, regulator( you changed this already tho?) or an injector. I'd personally hold off on messing w/ tps right away. Ensure the wiring is healthy and connector is clean, but otherwise that could drastically complicate an otherwise simpler problem 😕 My '96 didn’t show a code for the ICM. It'll register codes, soft or SES light, for the opti tho. Even tho you changed it - idle air control not flowing/ opening well enough when hot to meet the air demand, needs calibration? You changed a good few parts. If all done recently, with mimimal drives yet, maybe need to disconnect batt and allow the ecu to reset?
As others said, Scan for codes (you said no codes. Did that just mean no ses light, Or true obd2 scan?)
Fresh gasoline can work miracles too tho ✨️ 😉
Good Luck 👍🏻
Last edited by Torqsplit; Apr 20, 2026 at 01:41 PM.
BTW, you can pull that weather pak seal out of the back of the tps connector with a small pair of needle nose pliers. Straighten the wires a bit and put a dab of wd40 or whatever on their insulation so it'll slide easier, and wiggle it back out of the plug. Then you're not stabbing blindly and getting potentially false readings. If you end up checking voltages there 👍🏻
Heat soak affected my 1st ICM in warmer months. It cools down pretty quick once coolant starts passing thru the cyl head behind it again and will present as many other things. Tricky to diagnose. I'd start with verifying if fuel psi is bleeding off after sitting with a pressure guage. That's fuelpump, regulator( you changed this already tho?) or an injector. I'd personally hold off on messing w/ tps right away. Ensure the wiring is healthy and connector is clean, but otherwise that could drastically complicate an otherwise simpler problem 😕 My '96 didn’t show a code for the ICM. It'll register codes, soft or SES light, for the opti tho. Possibly a dirty idle air control not flowing/ opening well enough when hot to meet the air demand. As others said, Scan for codes.
Fresh gasoline can work miracles too tho ✨️ 😉
Good Luck 👍🏻
Injectors are good...brand new 24psi...car runs great. I have not changed my fuel pump yet, but I have a new GM one in the box ready to go. I spent a few months doing maintenance on the car so I figured why not? Scanned for codes: None. I did also change the IAC valve. What a pain in the azz.
Really Stumped At This Problem. Could Sure Use Some Help!
