I am not very mechanical, I do not know the complete ins and outs of the Third Gen Trans Am, and I haven't even had my car very long, so I don't really know if I'm on a wild goose chase or not.

I have an '89 Trans Am WS6 with the 305 TPI and just shy of 48K original miles. I am the second owner. The previous owner barely drove it (obviously). He said it spent most of its time in the garage, having been driven mainly during summers.

I thought I had a couple of pretty major problems fixed, but over $800 later, one of them seems to have resurfaced. My idle was really rough after the engine warmed up. It kept bouncing back and forth between 500 - 700, and it felt like the engine just wanted to quit. Then, two weeks ago, I broke down on a highway. On the last few drives before I broke down, I noticed that on the highway, when I would add power (OK, floor it), I would get a very sluggish response out of the engine and the revs dropped sharply right when they hit 3,000.

The mechanic troubleshot the breakdown to a bad fuel pump. For the idle issue, I asked him to do a tune up and replace the fuel injectors with a set of rebuilt Bosch III's that I bought from Southbay. He also replaced the air filter.

When I got the car back, the mechanic said he was not satisfied with the very loud whine the new fuel pump was making and he ordered another one which he is going to put in tomorrow. Other than that, the car ran GREAT!! The idle is rock solid and the car is a lot more lively and responsive.

Here's the rub. I had it out on the highway for an hour today. My goal was to really test out the car with all the "improvements" it got. For about 45 minutes, I did all kinds of driving. Sometimes I cruised at 70, sometimes I would nail the gas to pass other cars, and sometimes I gave it a good workout going about 95 - 105. Everything was going perfectly.

I was just starting to relax and gain a whole bunch of confidence, when the problem I had before of the degraded throttle response and sharp rev drop off came back. Nothing else seemed to be wrong though. The car cruised fine and responded well to mild to medium throttle inputs. The idle with the car stopped was still solid, even after the hour of mixed driving.

But what's up with the degraded throttle response and sharp rev drop off on the highway? I'm no mechanic by any means, but with everything else in the engine seemingly going right, could I possibly have a faulty throttle position sensor?

I also noticed something new after my car's visit to the mechanic. Maybe I never paid attention before, but my car's temp never seemed to climb about 160 degrees (or whatever the midway point between 100 and 220 is on the gauge) whether I was stopped or going. Today, with the engine idle in the parking lot for about two minutes, or stopped at a light, the temp climbed rather quickly to 220, but never went over 220. Then, when I'd start moving again, it would drop right back down to 160. Is this normal?

I have a theory that the temp never seemed to go that high before because one or more injectors may have been severely clogged or the spray pattern might have been off. The less fuel that burns, the less heat the engine will produce...right?

I sure wish I knew what the hell I was doing. I'd really appreciate some input!

 

To me that sounds like it could be the ignition control module. Mine has called it quits twice. The first time my car wouldnt go past 2500 rpms and when it did it would cut out and sometimes die. The second time I would be cruising along and the car would start cutting out while driving. This would happen after I have been driving 20 minutes or longer. The ignition modules dont like heat.

If your TA is not your daily driver you can take it out and get it tested, and you might as well get the coil tested too. Or just replace everything, plugs wires cap & rotor, coild, and ignition control module if you haven't done so already.

I bet its your ignition module though. If you do get a new one get the 369 module from GM. Any over the counter ones suck. Here are the part #'s

The acdelco # is D1943A the gm # 10482827

And for further education read this.

https://www.thirdgen.org/forums/di...tml?highlight= (048 to 369 Ign Modules?)

-Tony

 

Tony, thank you for the detailed information! Is the ICM something that I can wait on as long as I don't abuse the car, or is it something I need to do before I wind up on the side of the road again?

 

also if you are running the stock chip your fan will not work til the temp goes to 220-225 deg. Buy an adjustable fan switch and intall it on your left side fan, for the right side fan buy a 200 deg hyper Tech axilliary fan switch, it is located on you right side head. This will keep your engine cool even when you at a stop light.

 

Ehh...I wouldn't wait on it. If its starting to fail now then one day it will die all together. If your luck is anything like mine then it will be on the 5 freeway southbond during traffic on a 90 degree day. Then waiting an hour and a half for AAA. lol

If you can get it checked out first before you replace it. Autozone will do it for free. I dont want you to spend money on a part that maybe fine.

 

Thanks again Tony. I really appreciate all your input. I know a mechanic near my house that claims to be an AC Delco Parts Headquarters...whatever that means I happened to be at an auto parts store buying wiper blades and they priced out an ICM at $65. I didn't think it would be that cheap. I may just go ahead and do it before I break down. I'm tired of the side of the road!!

 

Thanks for the tip. Just a quick question though...isn't 220-225 a normal operating temp, or is it too high? The temp drops very quickly once I'm moving again.

 

no. besides the factory gauge is not very accurate, and the stock temp for the switch is upwards of 238 degrees. These cars were made to run hot from the factory.

both my cars, with stock gauges, sit at about 210-220 at operation temp.

 

yes 220 I believe is the normal operating temp, atleast its where my car used to stay at. The stock thermostat is 190 degrees, and the drivers side fan comes on at 220 or something like that. The passenger side fan only comes on when temps reach like 240 or you turn the air conditioner on. I have a hypertech chip in my car which turns on the drivers side fan at 170 or so, and I have a 160 thermostat in it and it stays at 160 unless i stop and then it goes up to 190. I noticed my car is more peppy when its 160-190 degrees.

 

If there's one thing I'm learning very quickly about the LB9, it does not do nearly as well under warmer conditions!!

 

Another thing worth looking into is what kind of fuel pump your mechanic installed....

There are great deals on some "high-performance" pumps out there, and some of them will set you right back to square one.

I went through 3 Walbro 255 lph in one year before I switched it out for an AC Delco EP-381 fuel pump. Its the one designed for the Turbo Trans Ams/Cyclone/Typhoon. Plenty of fuel on demand.

Before you buy the ICM (which I did too because I thought it to be my issue before), drive the car for a while to let it heat up. Then, as its idling, check the fuel pressure again to see if the pump is misbehaving. Mine would work fine on cold days, then start to die as it heated up.