1999 c4 hot weather issues

Hello all. Last summer I bought a 93k mile 996 c4, and it has been a total blast to own. This summer, im having heat related issues. Recently the car died at a stop light after idling in hot weather for a few minutes. Im saying around 95F outside temperature. Car started up fine and ran home fine, no more problems. So, I googled it, and most likely culprit was a faulty IAT on the MAF. I replaced the maf and air filter. Recently, the car seems really down on power in hot weather, and it died again. This time, in a parking lot, we were just pulling out, had to stop for traffic, and it just died. I can tell when its going to die because the idle goes to about 500, then bounces lightly. Any application of throttle does nothing, then it dies. Immediate re start, and we get going fine, but seriously down on power. She revs out all the way, and can even over rev, but getting into the power band is painfully slow, and it might or might not die when i stop for a light or traffic or what ever. Its summer and there are no cool days, so i cannot comment as to its behaviour in cooler conditions. Even at night here its fn hot. Had no issues like this last summer. So, hot weather car down on power and sometimes dies at stop light. So far has restarted fine. Have replaced maf. No smoke at startup, no bad engine noise, no leaks. I do know that 1 fan resistor is blown, so both fans work on high, but only 1 on low setting. It is tiptronic, and so does have the egas electronic throttle. No CEL. Thanks for your help!

Small update. I remember the trans slipping in the parking lot. Started out in 2nd as normal, but as we came to a stop from rolling very slowly, the trans slipped when i went to go, and thats when i stopped fully, and it died. restart fine, but revving slower as we try to maintain movement and airflow in mid town traffic. We were in hot weather earlier and it was reving slower, just figured running air conditioner and hot air made it slower, but even after turning off air cond, the power was down, revving slower than normal. Just had 100k mile trany and diff service done, and before this issue, it shifted great, firm. shifted great before service as well. Pretty sure when its not acting up, it still shifts fine. Its something that isnt noticed untill it gets off kilter, and this dying issue is the only time it has recently slipped a little in 2nd or between 1st and 2nd. Its done it perhaps 3 other times in the year, and only when really hot.

When all of this is occurring, what do your engine temperatures look like? In the normal range? Losing any coolant at all?

Quotes source post: 17571977

check the coils... seems you'd be getting misfires though... I had a similar problem last summer. Car ran fine when cool but after it warmed up, a couple cylinders would cut out...

Temp gauge gets to about the far side of the zero in the 180 mark. Last summer, it got hotter than that and never died. No coolant leaks. As for the coils, im not sure. if they work fine when cold, then they must be checked for failure when hot. I suppose its just as well to replace them. At this point, Im contemplating replacing the plugs, coils, crank sensor, and cam sensors. However, today, im going on a drive and see if anything else happens. Should have went earlier, when it was cooler. Unfortunately, all I have is a regular obdII scanner, and although it communicates with the car, its showing no codes. Wondering if its acumulative symptom. Perhaps, several things all contributing to a hot weather stall. I know for sure power is a bit down with AC on, so today, I will try to determine if power is still down with AC off, or if its all in my mind. No passenger today, so no need for cool comfort, and my drive can focus on feeling the car.

Where are you located? maybe someone close has a Durametric you can use and identify the issue

Had a similar problem with my 99 C-2. After running a couple of track sessions on a hot day the car would cut out, after trial and error of several attempts to diagnose failure and sending out the ECU for testing, I replaced the fuel pump relay and problem never reoccurred. Always carry and extra relay with me. Relay inexpensive and easy access under left side of dash panel.

I drove in mid day heat again yesterday. Got it to momentarily hiccup like 1 beat at a quick stop. I got home and kept engine on in garage and let temp get to far side of the zero in 180. In playing with air cond, radio it seems under very high drain conditions, the volt gauge drops to about 12.5 volts at idle. At this point, the idle does get a hair more stumbly, but at those temps its also idling slower, like 550-600 rpm. After playing with fans and such I put the battery on charge and it took 15 amps for about an hour then started tapering off. In about 3 hours it was taking a trickle charge at 3.5 amps. Drove again this morning before mid day heat, ran it hard when possible, then sat idling thru construction as well. Ran great, plenty of power, not running air cond, and temp needle never going past the beginning of the zero in 180. All I can say so far is the car dosent like hot days. I need to service the radiators and fans, and likely there is a component or 2 suffering from age and heat. Plan so far is to keep it out of the hellish heat, pretty much like I had known was a probable necessity given its a high strung 22 yr old sports car, but obviously forgot about recently. Unfortunately, previous service history is not on hand, so I will assume that anything that hasnt failed was never replaced. The trans fluid during the PPI looked like 22 yr old trans fluid for sure, but the car is a driver, so surely some little trinkets have been replaced here and there. I will throw a fuel pump relay at it. Ive actually been there with other cars, might be a long shot, but worth it for cheap and easy possible fix.

Will a durametric see things even if the ecu throwes no codes?

Quotes source post: 17575626

You may want to check battery condition and voltage output on the alternator.

Yeah, I was wondering if the battery and alternator are also suffering from age and heat. Likely a cumulative issue. Cooling, charging, sensors, ignition components, fuel pump. All systems that should need servicing or replaced by now.