JacksonJ

Here's the deal...

I have owned this car for a few weeks now...

2002 Trans Am (See Sig)

It has a random idle surge when I cold crank it with the AC on (I am not sure if I have troubleshot this issue with the ac off?). By random, I mean some morning it idles like a champ and other mornings it does this mess.


It does not do it in gear (not that I have noticed). Just a random cold start on a random day.

Troubleshooting so far... Removed and cleaned IAC, Cleaned TB, Reset IAC and TPS, checked for vacuum leaks.

Replaced Fuel Filter, PCV valve, Air Filter. Cleaned MAF. No Codes.

I do not have a diagnostic tool, simply a code reader.

When I unplug the IAC, the idle will smooth immediately. This leads me to an issue with the IAC, but it being random is throwing me off.

Any ideas or experience? I would hate to purchase the expensive little valve without exhausting my troubleshooting. I have been browsing forums for a couple of days. A lot of threads are built around cams, modified tb's, etc... Mine is bone stock besides an air lid.

In my previous experience I have been positive when replacing these or recommending a replacement. High idle, Low Idle or surging idle constantly.

This issue just has me stumped.

LS6427

iTrader: (2)

Unplug your MAF...start it cold......see what happens. Could be a failing MAF.

.

JacksonJ

You don't think it would throw a code?

If the MAF is healthy, you believe it will idle crazy and/or stall?

JacksonJ

I figured I would be getting Lean/Rich conditions and some sort of CEL if the MAF was bad...

JacksonJ

Unplugged the MAF, cranked the car, idled smooth...

wssix99

iTrader: (5)

My crystal ball tells me your problem lies underneath THIS ^ cover.


BTW - In our world, there are four clear signs of pure evil:

JacksonJ

Take your ball back to where you bought it... Lol... ac delco paper filter

JacksonJ

Unfortunately, the unplug the MAF test isn't reliable... It wasnt surging so technically there was no change.

When i was letting my car idle to cool it off before I left for work, the idle was surging. I unplugged the MAF... It kept surging.

Doesn't feel like a MAF at the moment.

JacksonJ

Thinking about what I am going to do this weekend to troubleshoot more.

I have a friend who works as a mechanic for Toyota, he is going to try and grab a scan tool for me to use, see if I can get some live data to look at.

I want to remove the TB completely and give it a good deep cleaning as well as look for vacuum leaks with more detail.

Due to the random nature of the issue, I don't believe there are any vacuum issues, but I have to eliminate it.

Any other suggestions?

wssix99

iTrader: (5)

I'd check your air temp sensor. (that should be easy to do with an ohm meter)

Do you have an automatic trans? If so, I'd also confirm if you get the surge in Park and in Neutral.

JacksonJ

I have a multimeter. I will have to search for the specs on the IAT sensor.

I do have an auto. I will get back to you on the park / neutral difference.

wssix99

iTrader: (5)

How many miles are on your torque converter?

JacksonJ

58,000 miles, all stock except for the lid.

JacksonJ

I went down the road this evening to grab some dinner and I made some observations that make this even stranger.

The surge seems to only occur between start up and getting to operating temperature. After it reached temperature, it didn't surge.

Hitting the brake made it stop. ( I pushed on the brake to put it in gear and test your neutral question, but since it stopped, I can't confirm that yet)

It only seemed to surge when the electric fans kicked on high and it pulled the rpm down suddenly. It's almost like this "kicks off" whatever makes it surge.

I tested voltage at the battery when the fans kicked on. I was at a steady 13.7 and the fans kicking on pulled it down to 13.0 temporarily before it came back up to a steady 13.4. By the time I got the multimeter out and my leads hooked up to test, the car was already warmed up and the fans kicking on no longer caused it to surge.

Is this not wacky or what?

JacksonJ

bringing the car up to temperature can throw open loop / closed loop into the equation, hitting the brakes draws vacuum from the engine, bad e-fans can over draw an electrical system putting strain on the vehicle.

I will keep making observations

wssix99

iTrader: (5)

I was thinking a cold, failing torque converter could start to get a little grabby, causing the engine to bog vs. surge - but at 58K miles, I'd expect it to be just fine. Still worth a try to see what happens in Neutral.

JacksonJ

I agree... I will try and confirm neutral. At that mileage though, its far fetched to be a tranny issue.

hrcslam

Could be the alternator. Next time it does it, disconnect the battery. If it goes away I'd look at the alternator or battery.

JacksonJ

On that note...

About 2 weeks ago I had the battery and alternator tested at a parts store. I watched the kid do the test. According to the hand held, both passed. Not sure how accurate the load testers are though...

hrcslam

Yeah a lot of times they'll pass that bench test, but right after start up, at idle, your alternator is charging the battery introducing a large load, then with your fans kicking on its running that's too. Plus the entire and any other accessories you have on like the radio etc. I dint know what they loaf test then to, if they load them at all, but it seems like the alternator is kicking in and off battery charge mode causing the engine idle to fluctuate. Can you read the IAC counts when it's doing the surging? Does that fluctuate too?