I should have known better, but couldn't resist. I now own a pristine 88 GTA, all stock, completely unhacked, and absolutely no corrosion. All the electricals in the car even work. But yes, it runs rough. It's a stock 350 TPI setup. The car always fires up great, then has a really rough idle. It does that in open loop. Once it goes into closed loop, the idle starts to drop really low, then surges, then drops again. The car does this a few times before dying. I can drive it even with that idle, but it runs rough. The car had a code 36 when I got it. I've changed out the MAF burnoff relay, and that cleared both the code and the SES light. Unfortunately that wasn't the cause of the rough idle/running. I have changed the IAC since the old one looked pretty bad. We've cleaned out the MAF as well. New plugs, wires, distributor cap, and rotor. So far I'm tending towards vacuum leaks, and I'm going to block off the EGR valve today to see if that makes a difference. I'm working through the list of obvious suspects on this one. This car is nice enough that it's absolutely worth the effort, even if it has to sit for a year or two while I figure it out.
Since I'm trying to weigh all my options here, my question to the more experienced gurus is whether anyone has done an EFI swap on these cars? As a last resort, that would be a possibility. But that being said, I absolutely don't want to lose the digital dash in this car which works great. Does anyone know if it's possible to have the standalone EFI work in conjunction with the GTA stock ECM so that the dash can function? Sorry if this seems like an obvious question. I normally work on carbureted cars (I own a 1977 T/A), and am a complete ignoramus when it comes to these cars and especially ECMs in general. Thanks!

 

Take a look at your TPS (throttle position sensor) and make sure it’s functioning correctly. Base setting should be around .54v and voltage should go up or down smoothly with the opening and closing of the throttle. Max voltage is around 4.50v at wide open throttle if memory serves. If voltage spikes all over when opening/closing your sensor is likely shot.

I also would do a smoke test to see if you have any vacuum leaks. A $5 harbor freight fluid exchange pump and a cheap cigar is all you need. Works excellent to track down leaks and seems to be more reliable than other methods as the TPI has some hard to reach spots if testing with propane or carb cleaner.

If you want a good video on this check out Jrobling on YouTube, a Google search with his name and TPS should pop it up. All you need to test is a voltmeter and some wire, it’s pretty easy.

I don’t have any experience with swapping to a modern EFI on these but considering how original and clean that car looks I wouldn’t go that route IMO especially if you want to retain the digital dash. Maybe someone else will chime in who knows more about swapping to modern EFI. I will say this that once you get TPI sorted out it’s a good system for a cruiser.

 

How EXACTLY is the PCV plumbed?

 

Reddragon88gta, thanks for the suggestions. We did check the TPS voltage to make sure it was at 0.54v, but I'll do another run through to make sure that it goes up and down smoothly with throttle movement. Right now I'm tending towards a vacuum leak, but haven't smoke tested it yet. Yes, the EFI option would be the absolutely last thing to do, since as you said the car is very original and clean.

 

sofakingdom, you mean is the PCV system any different than stock? It's the normal setup, with the valve on driver side having the hose go into the manifold. The hose is rock solid, but is still intact. That was one of the 1st things I checked.

 

I should add, last night we were rooting around and noticed that the wire connected to the EGR temperature switch (located under the EGR valve) was broken off. Not sure if that would cause these issues?

 

EXACTLY how is THE ENTIRE SYSTEM plumbed?

The side with the valve isn't what I'm getting at. Rather, the make-up air side.

 

Sofakingdom, honestly sorry if I'm being obtuse here. I want to make sure I give you a relevant answer. Not quite sure what you mean exactly by the plumbing of the entire system. As far as I can tell, the entire system is bone stock. I don't see any modifications out of the ordinary there, if that's what you're asking?

 

What I'm asking is, EXACTLY how the PCV system is plumbed. Not sure how I can ask it any plainer. As in, line starts here and goes there, another line starts somewhere else and connects to this thing, etc. Especially on the make-up air side. Photos would help.

 

Sofakingdom, guess I was overthinking it. As far as the emissions hoses go, they're identical to the sticker on the hood. Photo 1 is the hose from PCV valve on the driver side valve cover leading to the intake manifold. Photographs 2 is the hose from the throttle body on the passenger side leading to the passenger side valve cover for air in. Photograph 3 is the location of the air in hose on the passenger side valve cover (coming in from the passenger side throttle body).

PCV hose from driver side valve cover leading to intake manifold.

Passenger side hose from throttle body leading to passenger side valve cover (air in)

Close up of air in hose (coming in from passenger side throttle body)

 

OK, so looks like it's all still there.

Any rips/tears/splits/cracks in any of the parts that go to the pass side valve cover?

The hose that goes from the TB to the PCV valve all OK?

 

The hose going to the PCV valve, as well as the hose going to the passenger side valve cover seem fine, with no visible tears or splits/cracks. I've already done a couple rounds of carb cleaner, especially focusing on those hoses, and nothing unfortunately.

 

So we were able to at least solve the idle/rough running/running rich issues. The base timing was quite retarded. Car now idles great, and sounds great. And isn't running rich. However, while it is driveable, it still has a constant stumble at highway speeds. Also we noticed that disconnecting the ECM advance while setting the base timing didn't change anything in the idle, which seemed weird. Open to any suggestions from the TPI gurus. Thanks!

 

What about the intake piece that goes between the MAF and the throttle body? any rips/tears/cracks in that?

It is odd that the idle didn't change noticeably by disabling the electronic advance. It's usually something around 20 - 25° at idle. The ECM will maintain a constant idle speed but I'd expect the overall way the engine runs, even how it sounds, to be different. Butt hay, if it wasn't, it wasn't, and all the "expecting" in the world won't make it so, eh??

 

Thanks for the tip about the intake piece. Hadn't thought of that. I'll check that out asap. About the electronic advance, as you said, regardless of expecting a change, it wasn't happening. I'm just wondering if that means the spark isn't getting advanced as it would need to be at higher speeds, causing the constant stumble at highway speeds? Hopefully that doesn't mean the ECM going out if so.....