Rough idle
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Teching In
Joined: Jan 2022
Posts: 33
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Rough idle I have an 02 ws6 ls1 5.7 liter. Cammed, short tube headers egr delete, volant cai 6 speed manual transmission I recently flushed the coolant of Dex and added a 50/50 mix, burped the coolant system as well. I replaced a bad pcv hose assembly and the thermostat. I have a rough idle only on startup after the car sits overnight and it has stalled out of gear a few times. I am going to check the iac and tps sensors this weekend. I did clean the maf sensor with crc and lit it sit a few hours before reinstalling. As part of the coolant flush, I flushed and drained the transmission and it’s scheduled oil and filter change. The fuel filter was replaced about 3000 miles ago, from what I can hear the fuel injectors are firing, no issues with spark plugs after pulling a few, im thinking the fuel injectors may need cleaning so going to pick up some redline tomorrow when I refill. I did find a small leaks at the hose connection on the coolant crossover and it was repaired with a new clamp. No vaccum leaks that I can find, acceleration and drive ability is excellent only that startup. Shift is responsive, taking is good and clutch is responsive. Not getting any codes whatsoever. It almost feels as if the onboard computer is trying to learn, but I’m not certain. The car does have a tune. Am I going the right direction here or is there something I am overlooking? Spark plugs and wires are about 8k overdue other than that going to be installing an oil catch can.
TECH Regular
Joined: Dec 2005
Posts: 437
Likes: 9
From: Indianapolis
O2's are not factored in until you hit closed loop at operating temp set in your tune so probably 160~180f. The code they generate would be a heater circuit failing or it's not switching enough, if your car drives fine at normal temps after warm up I don't think it's that.
I would try unplugging the MAF and seeing how it runs on cold start up. It will set a code but will then discard the MAF data and just use your VE and idle tables eliminating MAF issues entirely. Since you're tuned we don't know if they tuned your MAF or not but you did change the intake which changes the calibration of the stock values, it shouldn't be that large but airflow is complex and can get uneven. It could have already been damaged before you cleaned it or the cleaning itself may have damaged it so it's easier to just unplug and rule that out. It's easy and free and crosses out a potential issue.
You really need a scanner to check your TPS, IAT, and IAC values, if you don't have one your really just guessing and winging parts and fixes.
I would try unplugging the MAF and seeing how it runs on cold start up. It will set a code but will then discard the MAF data and just use your VE and idle tables eliminating MAF issues entirely. Since you're tuned we don't know if they tuned your MAF or not but you did change the intake which changes the calibration of the stock values, it shouldn't be that large but airflow is complex and can get uneven. It could have already been damaged before you cleaned it or the cleaning itself may have damaged it so it's easier to just unplug and rule that out. It's easy and free and crosses out a potential issue.
You really need a scanner to check your TPS, IAT, and IAC values, if you don't have one your really just guessing and winging parts and fixes.
