Hi Guys,

Im frustrated now... finally solved the no start with a new ignition coil. At this point in time, after the car is started it runs at approx 1700 rpms then drops down to 1100. When it reaches this level it starts to loop. If I put it in drive and give it some gas it lacks power. Eventually the problem goes away after 4 or 5 miles but I was just curious as to if anyone had a solution or clue to what is causing this? I just bought new plugs and wires (gapped at 35) and a new coil.

What would happen if the Prom for the computer was installed backwards? Would the car even start? Not that i think that is the problem, just wondering......

 

You don't mention what type of induction system you got. Does any SES light come up or do get any codes?

My immediate reaction is you have an intake leak.

 

The prom in backwards would pretty much shut down the computer. The car would hang at a fast idle and run like crap since the car is just running off of some onboard hardware in teh ecm. Sounds like thats ok.

What kind of induction is this? MAF or MAP tpi, tbi? That will help alot in determing what the problem is. Also, do you have a scan tool or datalogging software?

 

Im assuming it is a MAP TBI....... i do not have a scan tool or datalogging software. The only code it throws is a 24 which is the VSS.

Would a couple backfires blow one of the intake gaskets?

 

ok today i started the car up and when it drops to 1000 rpms it starts to loop...... it will do this for about a minute or so and then drops, picks back up and starts to loop again...... the next time it drops it dies....... started the car back up and it is a high idle at approx. 2100 rpms. tap the gas and it remains the same will not drop to 1000 rpms.

A friend of mine has a scanner, but no connection for my year car so I have to search around for the boot.

Any other suggestions. It is still only pulling the VSS code.

 

Sometimes a "code" by itself can be misleading. Have you cleared the code (disconnect the battery) and then restarted to see if the code goes away?

It still sounds like an intake leak by the way it is behaving. I know a few people where the gasket under the TBI starts to leak. It's a quick and cheap fix.

 

I sprayed carb cleaner around the intake gasket and egr valve and no apparent change in rpms was noticeable. I didn't spray around the tbi gasket but will give it a shot.

I did notice however that when the engine warms up the surging or looping seems to go away. would this have anything to do with the CTS. I cleaned the IAC over the summer but i think it might be time for a new one. Also didnt know if the O2 sensor might have anything to do with this.

Car was running great before the coil went out and it backfired on me. Finally got it running and am now having problem with the idle and lack of power. I was leaning towards the "relearning the idle" but it just seems to be something else.

When I was changing the plugs, I broke the oil pressure sending unit, tried rigging it up but that didnt work. You wouldn't think this would have something to do with the idle problem?

 

you say you just change your plugs and wires? I know this might sound *simple* but check and make sure all your wires are properly set on your plugs and all connected in the right order.

 

Its possible for it to be an intake leak. Although usually a leak near the tbi base is just like opening up the throttle since its SD. If its bad enough itll cause a high idle and 0 IAC counts since the computer cant compensate for it anymore.

Assuming the plug wires and all that is in order, have you changed anything else? Lack of power and poor idle when cold could be due to a bad ignition module thats on its way out. Id go back and double check everything since the problems started after you worked on the ignition.

Neither pressure sender or switch will effect the idle, although breaking the sender near the intake will cause the gauge to go dead. The switch is mor for a backup switch for the fuel pump then anything else.

 

I took the cap off today and disconnected the ignition module. Ran it up to Advanced Auto and the module tested out fine. I also check the timing and all the wires are connected in the correct firing order. Any other suggestions?

It still surges when the idle drops to 1000 rpms. It surges for about 1 min. and then sounds like its about to cut out, then jumps back up, surges, then dies.

Ive checked for possible vacuum leaks and have not come across anything.......

 

Is this only an idle problem, or is the motor having trouble across its operating range? When it starts to surge like that, does pressing the accelerator cause the motor to just run at a fast idle, or does it still want to die or cut out?

 

I have given it gas after it starts to surge...... If i hold it at a constant rate, say 2500 rpms, it still surges. It will drop to 1500 rpms then bounce back up to 2500 rpms.

It isnt driveable. It is lacking power and will stall at stops or when shifting into drive or reverse.

The reluctor wheel (sits above the pickup coil) is rusted but doesn't have any noticeable cracks or anything to it. Do you think the pickup coil might be bad?

 

have you tried re-setting IAC and TPS?

 

I just cleaned the IAC, I cleaned it over the summer, but apparently not good enough. There was quite a bit of build up. Measured the pintle to the gasket and it was right at 1 1/8 in.

how do u adjust or reset the TPS?

 

https://www.thirdgen.org/newdesign/tech/tpimod2.shtml

you're lucky i'm in a good mood today or i would have told you to find it yourself keep us posted on this, my car used to have a slighter version of this.

It does sound like you might have switched two spark plug wires around, or if they were arcing. Or your new ignition piece (cant remember which you replaced) isnt working right. Wouldnt be the first time someone sold someone a bad part

 

The IAC cannot be reset. The computer does it automatically prior to parking the IAC after engine shutdown. I would leave the min air setting alone at the moment as its probably not an issue. The tps also doesn't really need to be reset unless the closed throttle voltage is excessivly high or low. The ecm takes the lowest TPS voltage reading and uses it as a baseline to construct a %tps reading so there isnt the need to adjust it. IIRC it was a problem on earlier cars but GM implemeted that in the ecm so it would be self calibrating. On some models the tps is non-adjustable. If you dont have a scantool, leave it be for the moment.

 

Ok, have you checked the EGR valve? Its the next thing on the easy fixers that cause big problems list. Itll cause big problems at idle, although under load the symptoms vanish as the egr is normally open there anyway. From that Id say that its probably ok but maybe worthwhile checking.

I might still suspect ignition problems or fueling problems (dead injector, failing ecm hardware, fuel pump on its way out, etc.) but its hard to diagnose a car without actually being able to see/feel/smell whats going on.

Also, can you datalog? Id say at this moment in time it might be worthwhile rigging up a cable and getting some datalogs so you can at least see what the computer is seeing. Might not tell you anything you dont already know, but then again the problem might be something stupid that jumps right out at you.

 

As for the rust, thats nothing to worry about. Id say if the car runs and the tach still follows the engine speed closely the pickup coil is working and there arnt any loose connections or anything.

 

The fact taht the car ran great before the coil problem still points to the possibility of an ignition problem. Id carefully check all the wires for damage and signs of arcing and consider getting a new ignition module. Theyre not too expensive and its worth a shot.

 

Mystery solved...... Im not sure which of the following cured the problem, at least I think it is cured. I will have to see how it starts up today after I change the oil and fuel filter.

Before putting the ignition module back on, I lathered it up with some dielectric grease just because there wasn't any on the metal plates. Put everything back together, made sure the firing order was right and the wires weren't arcing. Walked thru the entire engine and made sure all hoses were connected. Checked for loose grounds...... Everything checked out......

Took the IAC off and cleaned it up with carb cleaner really good. Took q' tips and cleaned the inside of the housing. Even though I did this over the summer, I figured it couldn't hurt anything. Put it all back together and let it sit for about an hour.

Said a quick prayer and cranked er' up..... she was sailing like a whistle. Started right up and ran at 900 rpms for about five minutes, no hesitation, looping, surging, nothing. Usually when I start it up, cold, it will idle high and then drop down to around 1000 rpms.......

The engine sounded great! was very quiet, the only thing that i dont understand is the whistling noise coming from the alternator?

So I guess if the problem comes back, I will know where to go now! Thanks for all the help guys!! You dont know how much this website has helped me......

 

If you are still having problems, I have found if the initial timing is set to far ahead of the value programmed in the chip (stock is usually 6 degrees) the car will surge at idle and be hesitant off the line. I have also notice that the stock O2 sensor can get lazy without throwing a code and will also cause the engine to surge.