'95 LT1 low idle problem

[Simon J]

Hi all,
I've been watching the forum for a couple of months and I have to say I witnessed a lot of nice builds and found great information.

I have a 68 camaro with an LT1 out of a 95 Camaro (as well as the T56 and four wheels disc brakes). The thing is when I start the car the idle is around 800rpm, which is good to me. But when I take it for a ride after one or 2 stops the idle drops to around 500rpm.

If I come to a stop too quickly it sometimes die (RPM drops too much) but most of the time it's just keeping a low RPM which is annoying at night with lights on or when the fan is on... I'm worried about burning the alternator with a too low rpm with accessories sucking juice.

Any clue what can be the cause or how it could be fixed?

Just FYI, I'm no mecanics, just an accountant with a car addiction

Thanks

[camrat68]

Need a little more information about your setup. Stock MAF, tuning, cam? Does it run well except for the idle? When was the last time the IAC was cleaned in the throttle body? Cleaning the throttle body would be my first step.

Jim
BTW-Both my Wife and I drive modded '95 LT1 Caprices on a daily basis. One of them with Camaro heads. :P

[Simon J]

Thanks Jim,

I bought the car with the engine already in it but as far as I know the engine is all stock (no tuning, no cam, stock MAF).
I does run well all the time. Even on idle it runs good, but the RPM is way to low.

I'm not sure what the IAC is, but I never cleaned the throttle body. What would be the best way/product to clean it?

Caprices are nice cars, the SS are fun to drive!

[camrat68]

This video should give you some ideas although they don't show the proper way to clean the IAC. I also forgot that the Camaro's had a slightly adjustable throttle position sensor.
https://youtu.be/S_ni39iwAys

Jim

[Simon J]

Thank you Jim,

Just watched the video. I'll be off for vacations in the next 2 weeks and make sure to clean the IAC when I'm back.

Thanks again, I'll update when it's all cleaned up.

[Simon J]

Just an update, I cleaned the Throttle body tuesday night and made a quick test drive yesterday. At first it seemed the idle problem was gone but then it came back but it's still way better than what it did before the cleanup

Thanks for the help Jim!

[Simon J]

Three years later the car is back on the road.
I parked it for the winter in November 2015 with a simple seal/bearing job. I ended changing seals/bearing on both sides, put new axles (twice...), changed the trunk floor and the gas thank. When I took the tank out I noticed that the vent was blocked on the tank.

I took out the car for a few test drives and the "dying" problem seem to be gone (the vent is probably what helps with that), but the idle still is around 550-600rpm. What would be the easiest way to adjust the idle rpm?
Again, that's a stock LT1 from a 95 camaro with a freshly cleaned throttle body and IAC.

I think the 95 was OBD I, is it possible to change the idle on the ECU via an app or a laptop?

Thanks again. The forum helped me a lot during those "off the road" years.

[Randy67]

A laptop, cable and software should allow you to set the idle rpm target. Probably HPtuners or similar would work.

[ULTM8Z]

My guess is the PCM is at least partially relying on the IAC to maintain the idle speed. So the idea would be eliminate that so you can adjust it manually yourself.

I did this on my Miniram’d Gen1 SBC with TPI electronics. Theyr’e both OBD-I, so my guess is the idle logic should be the same.

If you’re not up to getting all the recalibration equipment, you could probably do the following if you at least have a scanner and can monitor the IAC steps. You could probably even do it by “feel”.

While monitoring the IAC steps on the scanner (while at full operating temperature), start opening the throttle blades. The IAC steps should start to decrease. Once you get to zero, the ECM is no longer in control of the idle speed. Shut down and restart the car to ensure the idle is where you set it at (along with zero IAC steps).

At this point any additional opening of the throttle blades will permanently increase your idle rpm. Again, shut down the engine and restart it to verify it’s set properly.

If you don’t have access to a scanner, what’ll happen is this… you’ll turn the idle stop screw to open the blades, but the ECM will reduce the IAC steps to compensate (trying to maintain the programmed idle speed). So you’ll get a net effect of no increase in rpm (it may increase momentarily, but the ECM should bring it back down). This is something you'll have to just listen for (i.e., setting the idle by feel). At some point though, the ECM will run out of IAC steps to pull out and you’ll start actually permanently increasing the rpm. From there, simply set it to the RPM you want.

[Simon J]

Thanks guys! I will look into the "poor man's way", i.e. I don't have a scanner.
But I do have a laptop, so I might try to get my hands on a set of cable/software. I would guess OBD I are not so easy to find though.

Thanks again!

[ULTM8Z]

Check moates.net. they have all the OBD-I stuff. Also Tunerpro.net for the tunerpro software.