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Old 09-04-2010, 10:25 PM   #1
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What should be the correct Idle RPM?

1992 Camaro Z28, L98 Rebuilt with mild cam and Custom chip. The cam is : http://www.summitracing.com/parts/CC...8&autoview=sku

What should the car idle at when it's cold in park? It used to be like 900rpm.. And now my mechanic has it at like 1,500 idle in park.. And then you put it into gear, it's around 1,100-1,200 rpm..

The tach now is fluctuating from around 1,200 - 1,500 (needle and engine rpm) with car in drive is bouncing back and forth (along with the actual rpm of the engine) when the engine is at temperature.

No Cats.

Mechanics are always having problems trying to time my car.. They complain how it stalls when they set it correctly and then dies when they put it into gear (rpm drops).. Took them 45 mins just to set the timing..

What should it be at?


More information

Here is where the car RPM is at during certain instances:

Car is up to temp.

Transmission in DRIVE (with foot on brake but not moving) - 1,000rpm
Transmission in PARK - 1,500rpm

Turn car off and immediately turn car back on.
Car idles at 800-900rpm in DRIVE (brake on, not moving)
Car in PARK - 1,000
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Old 09-05-2010, 10:52 AM   #2
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Have you ever cleaned the throttle body?

Have you adjusted the TPS and the min idle setting?

Timing should be at 6 stock. I like to put a line of white out on the 6 line. Without the line, it's easy enough to see the teeth with your head down there and a flashlight. But when using the timing gun with the car operating (belt and fans moving), it's a bit harder to see without the white out.

In my experience changing the timing, if it's set at 4, it will want to stall out. It's WAY too easy when adjusting it to get it too far the other way. 12 with just a teeny turn on the distributor.

I've run my car at 6 and 8. I wound up putting it back at 6 and just leaving it there.

Cam specs:
1988-89... 207/213...415/430 (117)
1990-92... 202/207...413/428 (114)
Yours....... 206/210...450/480 (112)

That has to be the mildest aftermarket cam I've ever seen. Why so little? Anyways, it shouldn't have any measurable difference in your idle.

I cleaned the throttle body on my car at 60,000 kms. The blades looked clean when taking off the rubber air intake tube. But once I took the throttle body out and cleaned it out with brake cleaner, sheer gobs of black gunk came out. Idled smoother afterwords.

My advice is after cleaning out the TB, turn the idle screw up to raise your RPM's. Then adjust the timing to 6-8. Then go back and set the idle screw and TPS voltage.
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Old 09-05-2010, 11:16 AM   #3
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Original setting is around 6 or something but when the original mechanic (who I dealth with to get the engine rebuilt who sent it to another shop to actually rebuild it), they set it to 6 to break in the cam and engine and the car was HORRIBLE.. The idle was really choppy which sounded great (lope) but there was NO power.. I could barely go up hills.. It was if I was running on 6 cylinders.. No torque.. No power whatsoever.. I could even catch up to trucks, or buses.. Gas pedal had to be floored all the time to even move any type of speed.

I don't know if the "6" they mentioned is the 6degree or not but I was told for my cam I cannot run stock timing (6).
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Old 09-05-2010, 01:22 PM   #4
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Should probably pick up a timing light ($40-50) and the special tool for loosening the screw beneath the distributor ($4) and check for yourself what the timing is set at. There is an orange/tan wire by the air conditioning accumulator (big silver cylinder) that needs to be unplugged first in order to read base timing. If you don't unplug that wire, it will read total timing (somewhere around 20), which of course won't line up with the shark teeth degree markings down in the front of your engine. You just want to set the base timing.

Then you can change it around a few degrees and see for yourself where it runs best. 8 base timing should give it a bit more torque around town. Going higher than that, you may run into pinging issues. The $4 distributor screw tool is a MUST. Trying to get back there with traditional sockets and flexible extensions just doesn't work. It turns 45 minutes of grunting and swearing into about 1 minute of ease.

Taking apart the throttle body to clean it out, there is a pintle valve on the passenger side of it. If that valve gets gummed up (and they all do), it will get stuck in one spot. That valve needs to move in order to keep the idle right. It allows variable amounts of air to bypass the throttle blades (running cold) or close up and run all the air through the throttle blades (running warm). Mine was yucky. A spray can of carb cleaner will clean out the throttle body and the pintle valve and make it look like new again. If this hasn't ever been done, it needs to be done.

If you have a multimeter, you'll need to put the probes in around the TPS sensor wires (the top two wires if memory serves me correct). At idle, it should be 0.540 volts and moving the throttle blades, it should increase to 4+ volts. There are two torx screws on the side of the TPS that will need to be loosened in order to move the TPS angle around to adjust the numbers. If the TPS is bad, you'll never get a good idle. Mine checked out fine checking it at the TPS. But I wound up having some really bad drivability issues. High idle or idle wants to die with less than 40% gas pedal. Sometimes it would take both feet on the brakes to keep the car from moving in gear. I wound up driving it to the shop and the car would take off and accelerate to 30 mph simply by taking my foot off the brake and not touching the gas......The shop said that although the TPS itself was getting good volts, the computer was reading 0.9 volts at idle (way too high) and 1.5 volts at full throttle (way too low). A new ECM box and that was fixed. Thankfully a low labour cheap fix.

Last edited by Gord's Green Z28; 09-05-2010 at 01:25 PM.
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Old 09-05-2010, 01:50 PM   #5
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So step 1 is to clean out the throttle body and the IAC pintle valve with a spray can of carb cleaner. Let it sit for a few hours (or overnight) to fully dry. Screw the pintle valve back in all the way and put the throttle body back on the car. Turn the ignition key to RUN but don't start the car. You should hear the IAC pintle valve go "plunk." That's when you know it's back in it's preferred spot. Some people recommend starting the car for 10 seconds and then shutting it off to accomplish the same thing. But I like hearing it make the noise.

Step 2 is to adjust the min idle screw and TPS settings. Adjusting the min idle will change the TPS settings, so do the TPS settings last.

Locate the ALDL connector under the dash panel, in the driver's foot well area. Remove the plastic trim cover (if it is still there). Cut and form a paper clip into a "U" shape. Insert the clip ends into the ALDL in the 'A' and 'B' sockets.

Gord: I bought that $15 code scanner from Wal-Mart that plugs into the ALDL connector. It's a glorified version of the paperclip method. But it also comes with a booklet that tells you what any error codes you may have mean.


Turn on the ignition, but don't start the engine. This will force the ECM into its diagnostic mode. Wait 30 seconds to allow the IAC pintle to fully extend. Under the hood, remove the electrical connector from the IAC, then turn off the ignition and remove the paper clip jumper from the ALDL. With the IAC pintle fully extended (closed) all idle air will be controlled by the position of the throttle plates. Some manuals indicate that the EST bypass connector should be disconnected for this procedure, while some make no mention of it. While timing is a factor in idle speed, the EST should only operate as a function of engine RPM, temperature, and detonation sensor inputs. To remove all doubt, disconnect the EST bypass connector if your car is so equipped. Some TBI and V-6 engines do not have this bypass connector, and therefore must be set with no regard to the EST system. The EST can be bypassed on some cars by grounding the diagnostic terminal at the ALDL and continuing with the procedure, but the fuel mixture will be skewed to the rich side, affecting idle speed as well. In any event, the minimum air position idle speed range is wide enough to allow for some variations. As always, it is best to consult your service manual for the exact procedure for your system.

Gord: I left the EST bypass connector hooked up. So disregard the above part on that.


Locate the Torx screw on the left side of the throttle body. It may be equipped with a protective metal cap from the factory. (It's on the back of the throttle body on the driver's side up at the top.) This was intended to discourage adjustment. If the cap is present, use a small punch to knock it out. Once the screw is accessible, start the engine and place the transmission in DRIVE. Adjust the throttle stop to obtain 400 RPM with the transmission in "DRIVE" on an automatic transmission car, 450 in neutral on a manual transmission car, rotating the Torx screw clockwise to raise speed and counter-clockwise to lower speed. Once the idle RPM is set, place the transmission in PARK and turn off the engine.

Re-connect the electrical connector onto the IAC. Start engine. Idle speed should be governed by the ECM at approximately 600-650 rpm in "DRIVE" (for unmodified cars). Idle speed in NEUTRAL or PARK is less significant, and will be higher.

Gord: The above needs to be done with the coolant temperature at full operating temperature. When I adjusted mine, I set it for 500 RPM instead of 400 RPM (I have an automatic). With everything put back together, the idle sits at about 650-700 RPM at full operating temp. Maybe 800-900 when it's cold. Starting the engine with a cold start, it will jump to about 1200 RPM for a few seconds before settling down at 900 RPM or less (depends on outdoor weather temps)

Stock idle at operating temp by the way is 650 RPM.

After that, set the TPS voltage settings mentioned in the prior post. .540 volts is the recommended voltage for having the throttle body valves closed. You can up it to about .575 volts if you want, for a bit more torque feeling at slow speeds. If you start going into the .600 volt range, you can get an error code.
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Old 09-05-2010, 05:43 PM   #6
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im running the cam thats a step above, 08-302-8. 480/480 210/220 112. being my car is a stick this may not matter in your case but i have mine at 900 RPMs and untill we get the ez EFI on the car i have the timing down to 4' but thats also because my comp is bumped up to 10.41. i had an 8 thou shave done on hte heads (was needed) and a 20 thou shim gasket. needless to say this thing runs pretty good.

that cam is designed for no tuning needed and you should be able to stick to your stock parimiters. 6' timing and the usual way of setting the IAC.
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Old 09-07-2010, 12:50 AM   #7
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What do you feel should be what MY car should be set at in terms of rpm at idle in PARK, and in DRIVE (idling with foot on brake) according to my cam and it's specs? Thanks so very much for your assistance.
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Old 09-07-2010, 08:06 AM   #8
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like i said, being that cam reqs no tuning keeping in mind all you have done is the cam then i would go with stock timing and setting the IAC by way of the GM setting proceedure at 900 RPMs .
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Old 09-07-2010, 10:48 AM   #9
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Quote:
Originally Posted by quickchicken View Post
like i said, being that cam reqs no tuning keeping in mind all you have done is the cam then i would go with stock timing and setting the IAC by way of the GM setting proceedure at 900 RPMs .
Headers, Custom programmed chip, no cats, 1.7 rockers..
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Old 09-09-2010, 01:38 PM   #10
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Took to mechanic, they now have it at around

900-1,200rpm (In DRIVE)
2,000-2,500rpm (Immediately when you shift to PARK)

What SHOULD the car be adjusted to in:

DRIVE ?
PARK ?

Specs:

Engine: L98 5.7L V8 350ci. TPI
Rockers : Aftermarket 1.7 ratio.
Camshaft: CompCam 08-300-08 - 206/210...450/480 (112)
Headers : Edelbrock TES
Gas: Using 92 (Well 91 since all stations are 91 now)
Chip: Custom programmed (not a pre-done one)
Cats: None (removed cats)

I was getting Error 22. They replaced TPS, and now I'm getting Error 22 again.
There is also a quick hesitation while driving around 2,500rpm mark
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Old 09-10-2010, 06:24 PM   #11
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Maybe I missed this piece of info in all the posts but how is the mechanic adjusting the timing? ECM controlled engines use the IAC to obtain the desired idle RPM. So using a screwdriver is out of the question. The desired RPM can only be achieved by modifying the chip programming. Is that what he is doing?

As for what exact RPM the engine should be set to, the best is to go by ear (each engine is different). My ZZ4 cam didn't like anything below 700rpm (supposed to be 650 stock, IIRC) so that's where I programmed it at. Your cam doesn't seem to be too drastic either so 700-800rpm should be easy to achieve. Unless you have another problem.

Code 22 might not necessarily mean a bad TPS, it could also be the connector or wiring. Check the wires to see if they are possibly frayed by the connector and touching or if there's the blue wire is maybe shorting out on the engine.

Lou
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Old 09-11-2010, 10:12 AM   #12
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Quote:
Originally Posted by camarosource View Post
Took to mechanic, they now have it at around

900-1,200rpm (In DRIVE)
2,000-2,500rpm (Immediately when you shift to PARK)

What SHOULD the car be adjusted to in:

DRIVE ?
PARK ?

There is also a quick hesitation while driving around 2,500rpm mark
Man, that's gotta be one hell of a clunk shifting from Park to Drive. The idle RPM adjustments happen while in park (if doing it by yourself like I did). The idle RPM measurements need to happen in drive.

Just out of curiosity, what is your fuel pressure set at? Also, have you ever replaced the fuel injectors? Original battery cables?

How long has the idle problem been happening? Any changes before it started happening? Did it gradually get worse or did it just start occuring one day?
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Old 09-11-2010, 10:16 AM   #13
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Need to know your current measurements:

Base timing
Fuel pressure with hose disconnected
Ohms of the fuel injectors (if they are original injectors)
When the TPS was replaced, did they measure the voltage of it after it was installed? If so, what was it set at?
Original battery cables or replaced at some point in time?
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Old 09-11-2010, 10:16 AM
 
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