My TA, when started hot, has a reasonably poor idle, it jumps around 50-100 rpm. This only occurs when STARTED hot, and will go away after driving. The car isn't really any more difficult to start when this happens. If the car is hot, and has been running, the idle is fine.

Any ideas? TIA

 

It the idle after restart rough, or just wandering? If it is rough (like misfire), the mixture may be off due to injectors, open loop mode inaccuracies, or something else.

If the idle is just wandering but smoothly, I'd check the condition of the throttle body and IAC. The standard mode on restart is for the target idle to be higher, then slowly step down as the CTS and oxygen sensors warm up and start reporting cross counts. While in open loop, the ECM may have some trouble controlling the target idle if the TB and IAC are dirty.

 

i had the same problem and i ran a fuel rail flush on it at work (im a mechanic) and it fixed it right up. so far at least. now ive got some wierd power lock problem but yeah man...id try with that if u can. plus it cant hurt anything. if anything ull have some clean health injectors

 

If I had to guess, I would bet injectors leaking. Not only is it a common issue, but would make sense. On a cold start, the engine needs extra fuel, so its fine. Once warmed up, the car goes into Closed Loop, in which it can make fuel corrections, making it run better. On a hot restart, the extra fuel is not needed, and will idle rough until the car goes back into Closed Loop again.

Install a pressure gauge and start the car. Let it warm up, then shut it off and watch the fuel pressure. It should hold fairly steady (a few PSI drop in about 10 minutes is normal).

If it drops too quickly, I'd remove the fuel rail and prime the system and see if you can physically see any injectors drip fuel.

 

Vader, I think I understand, but could you clarify what you mean by smoothly? I'm guessing that means that they're not so sudden or irregular. Regardless, I'd definitely have to say its rough. The drops and jumps are very noticable.

I'm hoping its not the injectors. I just replaced them in July. Its not only the fact I just paid a good bit for the "new" set but the thought of taking off that plenum and runners again...

Let's see if can narrow this down some more...

New are the plugs and plug wires, the plugs no more than a month old, and the wires three weeks. The plugs a Splitfire that I got free at factory gap. The wires are Delco.

The injectors were used, 5,000 miles on them and cleaned by Cruzin' Performance. His tests indicated nothing was wrong in the tests he ran.

I cleaned the TB and replaced the IAC when I replaced the injectors.

A new knock sensor. It was replaced probably two or three weeks ago. Would this cause my problem, but operate normal otherwise?

O2 and CTS were replaced maybe a year ago, so there's the oldest here.

 

Goumba T,

Have you scanned for codes? I had a 32 (EGR) on my '87 LB9 and that caused all kinds of errant idle problems, stalling, etc.

The car sounded real mean, but ran lilke crap.

 

its pretty intermittent that it happens so...i doubt its a code and theres no light on...i know there still can be but...im gonna try that if my next thing doesnt work. i did a fuel rail flush at work and it seems like its just about gone. but the idles still a lil bad. so i got a cap rotor and oxy sensor.did spark plugs and wires earlier..

 

I also happen to believe some of this is inherent to the TPI design and heat.

I have used my cars as guinea pigs and several others that I know of that were either stock or modified and in tune and 100% operating order.

TPI cars when parked and are heat soaked in hot weather can have some stumbling and detioration of the idle. We have incredible amount of heat soaking and a lragwe large amount of alum. covering our fuel lines and rails.

I know this "shouldnt be the case" due to a return line in fuel system and a pressure rated at 43.5 psi but I have not found another logical reason.

On 3 cars that I tested on, I found that if everything else is the same and FP is raised to 48psi line off, the car does not exhibit these characterisitics. I credit this with the slighhtly higher fuel pressure stopping any heat related vapors form forming in the fuel lines or inj rails.

I have done a lot of testing on my Formula on the 350 and 383 and different new injectors. The 48psi fuel pressure solved the issue.

Want to see some crazy stuff slap a fuel gauage on a car with a returnless fuel system and watch the pressure spike on a hot retart :-) Dont laugh when u see 70 ro 80 psi, so my logic has some blind shots in the dark here:-) Also almost all new cars ahve fuel ratings higher than anything older. I also dont believe this is always the quoted issue fo higher atomization, I believe it might be part of that, but alot may be related to heat soak and related hot starting. Engine bays are more crowded and therefore hotter than older designs. Fuel is affected by heat and will do stupid things and even form into vapors and the like when heat forces it too. Just my thoughts and some things and trends I have found.

Further more I have experienced this on pure "stock" cars with only 17k on them

later
Jeremy

 

I just put a fuel guage on my T/A after letting it warm -up a good bit and shut it off....in roughly 30 mins. it went from 44psi to about 22psi..is that normal? car is stalling after it reaches a certain temp. but never fails to restart.

 

are these just really rough idling engines? i did the fuel rail flush on mine, fuel filter, wires cap and rotor and spark plugs....only things i can think of now is iac valve and the fuel pump. but..where is the iac? doesnt that require taking the plenum off?

 

I can set my coffee mug on the plenum and barely see a ripple.

"Rough" is what happens when one cylinder isn't firing, or isn't producing power on ignition. Pull a spark plug wire on an otherwise decent running engine, and it will get "rough".

"Unstable" or "wandering" is what happens when the RPM varies slowly up and down in a range.

There are various causes for either condition. Which one is plaguing you?

 

It honesly sounds more like you're surging, than running rough.

Just curious, did you notice the problem immediately after you're new plugs and wires were installed? Or later on?

Not saying this is what you did, but this is why I rarely throw new parts on an engine all at once.... because if one of the pieces are defective, or not installed properly it makes it all the more difficult to immediately pinpoint.

 

Later on. Nothing had been done within two weeks prior to this starting.

Vader, its not wandering. Its a rapid change. Being I've never had the experience, I'll try pulling a wire tomorrow and compare.

Yeah, I know, but I don't have a garage, so when the weather's good... sometimes gotta pay the consequences afterward. At least I didn't do that much and can narrow it down to 3 (if in fact something I did...)