Alright folks, my '89 Trans Am GTA 350 TPI has developed an issue, the details of which are as follows:

The problem began a few weeks ago as a surging idle that was most noticeable when the car was in D. The idle would surge around between 500-700 RPM. A friend of mine with some knowledge of small block 350s suggested the oxygen sensor might be to blame. Thinking to test this, I unplugged the O2 sensor and drove the old girl around for probably 40-50 miles. For the first 10 or so miles, the problem seemed markedly less severe....aside from the SES light blinking a couple times...something I expected due to the O2 sensor being unplugged. After this, the problem returned en masse. Not only did the surging idle return, but the engine developed a vibration while driving. I feel certain this vibration is due to a dead cylinder. I got the O2 sensor replaced, but it didn't clear up the problem. The surging in the idle seemed gone, but it still idled rough. The situation at the present is as follows: I start up the car after letting it sit till cold. It purrs like a kitten and drives smooth for about the first 5-10 minutes until the engine gets warm (seems to be until it is warm enough to go into closed loop). The dead cylinder (or so I believe it must be) then kicks in, and the engine feels quite rough while driving...the idle is also rough. If I turn the car off and immediately try to start it again it will not start and I have to use starting fluid to get her going again. However, if I let it sit for ~15 min and cool off she'll start up on her own again. Things I've tried so far (aside from the O2 sensor I previously replaced):

-Plugs
-Wires
-Had a compression test run (checked out good at 150/150)
-gave the old 'listen through a screwdriver' check to the injectors...they're all merrily clicking away like they should.
-checked the fuel pressure at the rail after the fuel pump primes the engine...sitting pretty at 45 PSI. (Have NOT checked it with the engine running).

My next suspect (as suggested by a friend) is the EGR system. Thoughts? Does this seem a likely candidate? Anything else I could check before getting a shop to diagnose it for me?

 

Any thoughts folks? Any input would really be appreciated...

One additional piece that may be helpful. I pulled the plenum off tonight and found an extra-crispy, melted closed vacuum hose that runs up into the throttle body...no doubt the hose was made crispy when I had a small, 30 second engine fire about 6 months ago (when I was first getting the car running). Could the crispy hose extrordinaire have anything to do with this problem?

 

Bump...are there really no ideas on this?

 

When you find out please let me know.I have a 90 305 doing same thing

 

I'll certainly let you know...I wound up taking it to a Garage I trust...didn't want to keep just throwing money and time at it...

Stay tuned for the outcome...

 

I already did fuel pump and oxygen sensor thing.Modified air breather,put chip in IAT,put different TBI on it.Plugs and wires....I give up at this point,drive my truck for a spell.

 

OK So...I got it back out of the shop.
* They replaced the intake manifold...said the old one was in bad shape.
* They also corrected a bunch of vacuum leaks that could have been hampering performance.
* They said my injectors need replacing, but that it would cost them $110 a pop to order them. So... I'm going to keep an eye out for a good used set and see if I can snag 'em for cheap.

The engine does run better, but - ironically - none of what they did fixed the problem I took it in for - the vibration. I took it to get the tires balanced yesterday, and it turned out the vibration was caused by a bad U joint at the front of the driveshaft. Go figure! The U joint has been replaced and the drive is already much better. Now all I need to do is replace the injectors to get power back up to par and we'll be good to go!

 

Ok,great.I have a extra set of stock injectors for 20 plus shipping or you can go to local Pull A Part and get your own.Forget all that high dollar mumbo gumbo for a stock motor.20 bucks is what they cost me and work just fine.

 

Weelll can't say the forum was a whole lot of help this time around but for anyone who happens to come across a problem similar to this, the main source of my engine performance troubles turned out to be the fuel injectors. A new set for ~ $150 from http://southbayfuelinjectors.com/ and a few hours of elbow grease to put them in, and we're good to go again. :-)

 

I had the same exact problem about a week after your last post, didn't see your thread. Turned out to be my injectors as well. Wasted some money on ignition parts I didn't need, but fortunately I didn't have to pay someone a bunch of labor for it. Your symptoms didn't seem to reach the final stage of having the engine turning off on you and not restarting for two hours (just like a bad ignition module). I bought injectors from FIC, installed them and viola it's a new car again.

 

I think it's important to stress for anybody else who experiences a problem similar to this on a TPI that the injectors are a likely candidate, especially if the car has 150K+ miles on it and the injectors have never been replaced. They tend to start going bad around 160K, and cause performance problems like the ones described in the above posts.

Edit:
Even if the injectors aren't bad yet, replacing them is good preventative maintenance after that many miles, so it will still be money well spent.
A couple of good places to shop for replacement injectors:
South Bay Fuel Injectors - http://southbayfuelinjectors.com/
FIC - http://www.fuelinjectorclinic.com/
Both places offer quality remanufactured fuel injectors to fit a variety of 305 and 350 TPIs, including L98s, LT1s, etc.

 

I think it's more a matter of physical age. Allot of people are experiencing this right now, and I don't believe it was that large of a problem even just a couple years ago. My car only has 22K on it and it still had bad injector(s). I will say that my car had no problems until I poured a can of "Gauranteed to pass" into the tank. I'm sure I didn't need, since it passed the dyno emissions test with flying colors. But after a couple of days, I started having symptoms. I'm wondering if that stuff contained something that damaged the injectors.

 

Following up. After doing some more research, I really think the "Guaranteed to pass" stuff is what ruined my stock injectors. It seems that the Multec injectors are designed so that fuel flows over the coils to coil them. It also appears that many injector cleaners can cause damage to the insulation on the coils. My car was fine until I poured that stuff in the tank. Two days later (and only about 20 miles) and the injectors are shorting out. I should send them a bill.

http://www.corvettefever.com/techart...n/systems.html