Idle RPM: V6-2.8

[85_Olds_Ciera]

Are there any charts giving specs for Auto/Man transmissions?

Specifically, 1988 Beretta with Auto...

What about spec when in neutral/Park for Auto?

[merlot566jka]

not adjustable.....computer controlled. what seems to be the deal with it?

[geoffinbc]

Agreed. If the ECM is happy at a hot idle it should be in the 800RPM range for an auto. A manual will be almost 1000RPM.

[85_Olds_Ciera]

not adjustable.....computer controlled. what seems to be the deal with it?

88 Beretta Service Manual Supplement suggests it is adjustable (pg. 6E3-C2-11).

I'll have to use my relative's OCD reader to do it, for reading RPM, but the main steps are to put the IAC Valve in a specific position, and then adjust the idle stop screw (which is covered up, and cover must be removed). The TPS must be within its range before doing this adjustment.

All they list is RPM in drive (550 RPM) and for manual (600 in neutral)

88 Beretta I own appears to idle in neutral around 1,000 RPM (digital tach says so)..but I will need OCD to confirm this idle speed and TPS voltage.

Hence, it appears someone has messed with this adjustment, and got it wrong; you need the Service Manual to know what to do....winging it will get it wrong.

I recently replaced the timing set, water pump, valve-covers, and after putting it all back together over a two week period, I came up with a plug that I can't plug into anything on firewall side of motor...I don't think it was plugged into anything when I tore it down...but the two wires on this plug have the same color coding as two wires on the IAC valve, and the Service Manual talks about grounding a diagnostic "test" terminal to put the IAC valve into a specific position....which I suspect is this plug.

[merlot566jka]

idle is controlled by the computer via the iac. if your idle is around 1000rpm you have a leak, faulty iac or more problems. use some carb cleaner and spray around for some leaks. clean the iac and replace the gasket.

the grounding of the testing terminal is actually the aldl, when you ground it it closes the iac.

the idle is set from reference of the tps. from there it uses fuel trim and other data to set the idle in the iac. it uses 'steps' or 'counts' to control the iac. map readings also help set the idle. a high idle is usually because of vacuum leaks, faulty iac (could just be dirty), or incorrect data from one or more sensors. use the iac relearn procedure if you suspect the iac is out of calibration. as a side note, ive never had to use the iac reset procedure. check your crankcase breathers and pcv...and your valve cover gaskets.

if the idle set screw is still sealed, dont mess with it. it is fine the way it was set from the factory. there must be something else wrong if it is still sealed.

[85_Olds_Ciera]

idle is controlled by the computer via the iac....

Hey, I bought a 1971 Vega when they were new, and now I'm rebuilding a 1988 Chevrolet Beretta with a 2.8 V-6 engine...but it appears both were "lemons." Here's what one mechanic says of the Beretta:

Even the technicians at the large Chevrolet dealership near our shop tell us that they try to run from them (1988 Chevrolet Beretta with a 2.8 V-6 engine) whenever they come in.

I'm going to have to bone up on this GM vehicle, for instance, he further states:

...Immediately, GM had some sort of problem with this arrangement. They began manufacturing "speed density software" to update these vehicles. This speed density software consisted of a new prom, a new idle speed control motor, and a label to attach to the ECM (computer) that the vehicle had been updated with the speed density software. I am unsure of exactly what this corrected, but it told the ECM to ignore all signals from the MAF sensor. The MAF (mass air flow) sensor was still there, it just didn't do anything anymore. It presents problems for a repair technician if he is unaware of whether the vehicle has been updated or not. A scanner plugged into the ALDL link will give erroneous data and trouble codes if the vehicle has been updated and the scanner is not made aware of it!

Thanks for the come back...but I'm going to do some more research, before throwing $$$ at it...

[85_Olds_Ciera]

(if) it was set from the factory. there must be something else wrong

Have to get another manual for this matter: which I just bought.

1987-1988 GM-Wide Driveability and Emissions Diagnosis & Trouble-Code Manual for 2.8L VIN W Speed Density Engine #75841

GM's update, Speed Density Software, is what a person needs to know here.

[85_Olds_Ciera]

the grounding of the testing terminal is actually the aldl, when you ground it it closes the iac.

You mean when you use the Poor-Man's Code Reader, this is grounding it?

thx

[geoffinbc]

I have worked on a few manual trans cars and they all idle just under 1000RPM according to the tach. On my buddies Cavalier the desired RPM (read with a Tech I scan tool) and actual RPM were within 50RPM all the time in either direction and it was nearly 1000RPM. Mine idles at 950 and I can never change it. The ECM always commands it there.

[85_Olds_Ciera]

...the desired RPM (read with a Tech I scan tool) and actual RPM were within 50RPM all the time in either direction and it was nearly 1000RPM. Mine idles at 950 and I can never change it.

Ok...thanks...when I get that service manual, I'll see what they have to say...mine is around 1,000 in idle neutral/park, and it seemed a pinch high, as based upon other vehicles I have owned/driven.

[85_Olds_Ciera]

actual RPM were within 50RPM all the time in either direction and it was nearly 1000RPM. Mine idles at 950 and I can never change it. The ECM always commands it there.

This is new to me, but I found this tidbit for 747 ecm, which may/may_not exist in my ecm:

There are additional factors that affect the IAC position. If the battery
voltage dips, the IAC can increase the idle. The A/C turning on, or
decel fuel cutoff (DFCO), can affect the current IAC position.

For an idea of how these factors can work, I'll use the A/C turning
on as an example. With the engine at IAC controlled idle, and the A/C
turning on, additional steps are immediately added to the current IAC
position. Another table value also adds to the desired idle rpm. Lets say
the desired idle rpm went from 800 rpm, to 850 rpm.
============

Hence, idle may vary, for one reason or another...

[85_Olds_Ciera]

The ECM always commands it (idle) there.

Correct: GM Service Book says,

"If the IAC valve is unable to control the idle speed within 100 RPM of the ECM commanded speed, a Code 35 should set."

[geoffinbc]

Yes and that would indicate a bad IAC, or vacuum leak. Could also indicate leaking injectors.

[85_Olds_Ciera]

Agreed. If the ECM is happy at a hot idle it should be in the 800RPM range for an auto. A manual will be almost 1000RPM.

I used a Snap-On Scanner quickly today, for the first time, and it showed the OEM idle (reference idle) spec...I assume it is a valid entry.

Was looking for other data points...so I just glanced over this value, which was somewhere in 800 range.

Had other tasks to do, so I by-passed this topic...but since I know someone opened up the plug to re-adjust throttle position, I rather suspect someone has twitched idle on this twenty year old vehicle before....

This vehicle is suppose to have Speed Density Software installed, but I could read the MAF...but have no idea is this value is being used or not...still have not received the book I ordered on this topic.

[85_Olds_Ciera]

idle is controlled by the computer via the iac. if your idle is around 1000rpm you have a leak....

calibration. as a side note, ive never had to use the iac reset procedure.

Tidbits:

I received the 1987-1988 manual on Speed Density Engine (Vin W: 2. . and reading to date only indicates this tidbit:

Idle Learn Procedure:

1. Install Tech 1 "Scan" tool
2. Ignition "ON," engine "OFF."
3. Select "IAC SYSTEM," then "IDLE LEARN" in MISC TEST" mode
4. Proceed with idle learn as directed.

This procedure allows the ECM memory to be updated with the correct IAC valve pintle position for the vehicle and provides for a stable idle speed.

So, it appears there is a way to teach ECM...otherwise, I wonder how it learns?

I did use a can of ether, and found there were vacuum leaks around upper-intake gasket, EGR's "push-rod," and I will have to check around PCV valve...but, as cold as it is, I won't get around to fixing them until next year.