1988 Beretta GT Rough idle when "cold"

[3X00-Modified]

best info I can find, so I guess any 89-90 with the 2.8 will work as long as the transmission is the same, as far as finding that, I have no clue... Best bet is Car-Part.com but then you would need it shipped to you. You could have it shipped to someone in the states and they could forward it to you as well.

Upgrading your 1988 Beretta to Speed Density (Eliminating the MAF)
October 27, 2005

If you have a 1988 Beretta with a 2.8L V6, you might notice a MAF sensor in your engine bay along with the MAP sensor. This is because the 88's were setup to sense engine load and map fuel based upon both of these sensors as opposed to just the MAF sensor -- why you ask? The system used on the MAF cars was problematic and sometimes trouble codes were incorrectly indicated. Anyways, to upgrade your car to be 'Speed Density' which will delete the MAF and use only the MAP sensor, you will need to do the following:
Locate and install a PROM (memcal/chip) from a '89-'90 Beretta (to avoid issues with your EGR - auto or manual shouldn't make a difference)
Remove your MAF sensor (it was robbing power anyway)
Splice in an IAT sensor from most any other year Beretta model (they're pretty much universal in the GM world) in place of your MAF sensor.
Wire the IAT sensor up to the black/red and black/pink wires you cut the MAF sensor from. The other 3 wires are no longer used and can be taped off and put back into the wire loom. On the IAT sensor, there will be a black wire and another colored wire -- the black is the ground, so wire that up to the black/red wire. The other wire is for power and you'll want to wire that up to the black/pink wire.

That's all there is to the upgrade. If you're having trouble locating a suitable PROM, your local GM dealership should be able to help them out -- just let them know what you're trying to do (there were service bulletins out about this). Ratings from GM show a 5hp increase in 2.8L equipped vehicles from 1988 to 1989 -- most would say that the MAF delete is the reason.

[zcylex]

about the shipping to me theres no problem as i have a forwarding company at miami that sends stuff to me via plane or boat. about the speed density update should i just look for a 2.8L PROM from an '89 with auto transmission then?

[3X00-Modified]

That would probably be your best bet... since those came with the speed density chip in them. Double check with the JY though that the EProm is still in it... some are removed when you search for just Engine Control

[ifixalot]

with no IAT at all and only the wires, I wonder if it running way rich when cold until the oxygen sensor heats up and tells the computer it's too rich.
Then it leans out and runs fine.
Here is a chart of IAT at various temperatures. The colder it gets, the higher the ohms. Open circuit would indicate to the computer, it's extremely cold outside.

http://www.google.com/imgres?imgurl=htt ... CD8Q9QEwAw

[zcylex]

finally got a "ARCL" PROM from a 1989 Beretta 2.8L with auto transmission

@jskiguy thanks for the suggestion but that is highly unlikely normal ambient temperature here is 33 Celsius and a regular day and it gets up to 41 Celsius outside on hot days. and at night the lowest we get is 20-23 Celsius there's a MAT sensor on the MAF that works as the IAT measuring intake temp.
the O2 sensor has already been replaced. the IACV is NOT getting any signal from the ECM we checked the wires and they are fine just IAC never moves or does anything.

according to my repair manual voltage on iac should be about 5V but it never gets there. 1.5-3.8V max we opened the ECM and found some damage on the logic board so next step is to replace ECM, the PROM should be okay but im replacing it mainly because it doesn't have the speed density update.

[3X00-Modified]

I think with that combination you should be back in the game.

[zcylex]

sure hope so i want to do so much to this car but if its not working correctly it wouldn't be worth it lol

[ifixalot]

You missed my point, yeah it's warm where you live I get that.
IAT is "intake air temperature" sensor. So if it has none and just the wires and connector as you said,
the computer thinks it is freaking cold outside and it richens up the mixture as it would if it really were cold outside.
You say you have a built in MAT on your MAF but that is not how your car was originally wired.
Good luck to you

[zcylex]

i understand what you said but if you go back to that post the sensor that is NOT present is the one in front of the radiator and i later found out it was ambient temperature sensor that sends info to the digital dash info but not to my analog.

the MAF in my model consists of two sensors, one that measures air flow and the other measures INTAKE AIR TEMP or (MANIFOLD AIR TEMP). so its the same thing different name...

PS: im trying to gather as much info from my alldataDIY manuals to post em here soon it would help people diagnose better this kind of "Rare" problems lol

[3X00-Modified]

You say you have a built in MAT on your MAF but that is not how your car was originally wired.

Yes, that is how his car is originally wired. hence why you need to ADD an seperate IAT sensor when doing the Speed Density upgrade because you remove the MAF and it's part of it.

[zcylex]

is the IAT mandatory? i mean can i use the already built in MAT sensor instead of the IAT?

offtopic:

regarding another mod i want to do, can it put the GTZ turn signals and fog lights into my front bumper ? i've seen they are separated in that model can i do that too?

[3X00-Modified]

You could but that MAF sensor is a decent restriction to the intake itself... Grabbing a two wire IAT makes the install much simpler to deal with.

[Rettax3]

is the IAT mandatory? i mean can i use the already built in MAT sensor instead of the IAT?

offtopic:

regarding another mod i want to do, can it put the GTZ turn signals and fog lights into my front bumper ? i've seen they are separated in that model can i do that too?

IIRC it was actually part of the standard GM procedure to use the MAT in the MAF -you know GM wouldn't want to pay for an extra part for their customers, just to correct a problem they designed and sold in the first place...

[3X00-Modified]

I like how people think that the MAF itself is an issue.

[zcylex]

I should rephrase my question:

Do you guys think my maf/mat will work with the new PROM/ecm (which im hoping comes with the speed density update) at least for testing if my issue is fixed. So i can start fixing modding and what not! ?

Ps: nobody replied to my offtopic question perhaps i should make a topic specifically for that lol


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