klumb15

my idle is all messed up on my car, i have no idea what is wrong with it...i just got a new computer and MAF sensor put in because the shop i brought it to said this might help because i still had a 5.0 computer in it and NO MAF sensor...well the computer and MAF didnt' help my idle very much...it idles alright when its cold, but when it gets hot, it is rediculous....when i'm sitting at a stoplight, it drops down to like 250, bumps back up to 500-600, then drops, goes up etc....it is like its strugling to keep running. Sometimes, very seldomly it clonks out on me...I have no idea what is causing this, I thought maybe some of you would, its driving me nuts tho..

aklim

You have a 350 higher compression motor and you are running a 305 computer? Maybe there is your problem. If you were speed density, you wouldn't have a MAF. Adding one is not going to help unless you have a defective one.

klumb15

no....i got a 350 vette computer now...it went in the shop because it didn't have a MAP or a MAF sensor...because in 86 the motor had a MAP, so there is no MAF for the new motor...so what the shop did was put in the 350 vette computer, put in a MAF sensor, and ran the wires for the sensor...i just spent 450 on that, so i'm kind of hesitant to bring it back right away...i talked to the mechanic and he was saying it could be an ideler controller or something that could be bad....i was thinking maybe a dirty or defective o2 sensor, because i heard sometimes that could cause it to struggle at idle...what do you guys think??

aklim

I would talk to Jeremy or Eileen at www.fasterproms.com because they deal with ECMs and are very familiar with the differences. You may or may not be able to swap ECMs or is it EPROMs in the way you mentioned. AFAIK, it would need a pin change at the very least to change a car from SD to MAF. If you didn't have a MAF or MAP, how did the ECM measure the incoming air?

klumb15

well the 5.0 motor required a map sensor....the intake had the map sensor in it, but it was gutted out, then the wires were just snipped and there was a plug in the hole where it measured the air...the mechanic said he was surprised it was running as good as it was when i brought it in...he said its NOT measuring any incomeing air at all....so then he put the new 90 computer in it that had MAF like the engine is supposed to have and he ran a new MAF sensor and wires...

aklim

Wouldn't it have been better to put in the MAP sensor plug and the MAP sensor? When he wired it up, did he verify pin out conditions? 91 and 92 Vettes had SD and previous years had MAF. So he just cut and pasted items he didn't understand in some vain attempt to get it to work and now YOU have to figure it all out? Good luck. I'd get myself a mechanic that really knows what he is doing

What of the EPROM? Where did he get that from? Was it a SD EPROM or a MAF one and what year?

90rocz

In 1986 the car would've came with a MAF not a MAP set up. It wasn't until 1990 that the Z28's came with Speed-Density or MAP set up.
You could'vre either kept your old harness and plugged into the new motor, or plugged the new engine, harness and ECM into your car.
If you have the 1986 ECM, you'll need the MAF sensor and wiring, if the 1990 ECM you won't need the MAF or wiring, just the MAP on the plenum near the distributor.
Until you get this straightened out(MAp and MAF thing...)It will never idle right...IMO..
M.A.F.= Mass Air Flow, or using a large sensor in the inlet air plumbing to measure airflow by a thermal-couple cooled by incoming air changing its voltage seen at the ECM measure in grams per second.
M.A.P.= Manifold Absolute Pressure, uses a small sensor mounted on the plenum near the distributor open to engine vaccum. Changes in engine vacuum(loads) are paired to the Speed sensor inputs and compared to preset tables in the ECM for fuel and timing corrections.

klumb15

oh boy it looks like I got a huge problem here....i know its a MAF sensor because it has the screen in it, and the board and everything....what was in the car was a gutted out MAP sensor....he got the new computer and it required a maf sensor, and i trust him because he did a TPI swap into his dads 46 truck or something...so he's been through this...i have no idea what he did with the prom or anythign like that...i took it back to him and was like hey man its still running like ****, can you do something...and he was telling me it could be a idler actuator or something that could be bad....i dont' want to take it back tho anytime soon and spend another 400 or 500 bucks...this computer **** is getting rediculous....why can't we all just have carbs..i'll get it worked out this winter hopefullly..see the thing is we don't even know for sure its a 90 vette motor!!!because the previous owner died when he owned the car, and his son sold it and didn't know jack **** about it...we got somewhat of a deal on it because we didn't know what we were getting our selfs into...we'll get it worked out this winter when we pull the motor and can identify it propperlly..

aklim

IIRC, the pinout on the ECMs are different between MAF and MAP so it is not just a plug and play operation. For example, the KS is different between an 87 and a 91. So, this leaves you behind the 8 ball. You had a mechanic that had a bright idea and now you will have to pay the price. Your mission, should you choose to accept it is to do one of 3 things after first deciding if you want to go MAF or SD:

1. Bring it to a real professional and pay them to fix the problem

2. Get a service manual and check every wire as to where it should go to the ECM.

3. Throw good money after bad and have your "mechanic" see if he can fix it although, it sounds to me like he has already given up but made you pay the bill.

aklim

We know there is a MAF between the intake and the TB. However, what we don't know is what he did to attempt to make it work. His dad's 46 anything did not come with fuel injection. Therefore he did not do a swap. He did an install, which is something totally different. All he did was dump the motor in it, hook up the harness and drove away. That is something so straightforward, a monkey could probably do it. Idle Actuator???? There is an Idle Air Control motor, aka IAC. How does he know it could be bad? Sounds like he is trying to cover up his mistake and charged you $400 for it.

Carbs are something I don't understand. I do know that drivibality is not as good with a carb as an EFI setup. For instance, I doubt I could run my combo in winter and summer without making some changes every now and then.

I don't care where the motor came from. If the heads are aluminum, it is probably a Vette motor. If not, it isn't. Plain and simple. Anyways, that is not your concern now. You should have asked us what to do before letting this butcher's apprentice get at your car. You really don't care right now what motor it is. IMO, I would get it converted back to SD because you are going to have to see if he got the MAF relays right and what not. SD is simpler for you. Check the pinouts and go with that. I hope you have your old ECM back.

He doesn't know his azzhole from a hole in the ground.

90rocz

Was this car originally a TPI (Tuned Port) car?? Or carbed??
If TPI, It only came with: 305ci, 19#injectors, 48mm Throttle Body, 58cc heads, MAF(Mass Air Flow) sensor between the throttle-body and air filters, 190 hp (detuned from 1985-smaller cam)TPS =0.54v@idle 4.5v@WOT.

Just put the 1986 parts back together for your car, the ECM, wiring etc..

aklim

I don't think you can put it all back without knowing what he did with it. It would take some patience and a DVOM to figure it all out

klumb15

yes the car was origionally a TPI car, but it was a 5.0 TPI....i'm gonna take it back to this mechaniac and he better stand by his work, i'm gonna be pissed if he charges more....i already have 500 into a computer that doesn't work...

merlyn

in your signature it say's "emissions deleted"...here's more food for thought...in this $500 computor job (cough,cough)...did you have the prom re-program'd as well..to remove the emissions...it will never idel right if you did'nt.

klumb15

well the emisions aren't completely deleted..the air pump assembly is still there, just the belt isn't running it, and the cat is cut out, but all of the wiring is there...besides i'm not getting any emisions codes, and the check engine light stays off when the car warms up...it goes on once in a while for about 3 seconds just after i start it up...