ok this is going to take some time to put down. the car is an 89 with a built 350 TPI and auto trans. the build specs do not matter for the problem this car is having. the car has been running perfectly for quite a while until recently. all the problems started when the MAF that was on the car(i believe it was stock, this is friend's car so i am not certain) was removed. the wire was damaged when it was removed and the MAF was replaced with a rebuilt autozone bosch unit. the car has not run correctly since. i happen to have a 87 with a factory MAF on it so that was swapped into the rebuilt units place. it runs better but is still not correct.

whats happening is a number of things but basically a poor and rough idle. sometimes the idle wants to hunt a little. normal idle is 900-1000 sometimes itll raise up to 11-13 on its own. sometimes the idle speed is fine for normerous starts and coming down from speed.

hard starts occur sometimes as well. youll go to crank the car and it turns over and over and it smells as if flooded. floor it while cranking and it fires right up. seems to do this mainly after sitting.

block learn can vary between 112-118 usually it starts out about 118 and drops from there to 112. give it some gas and it goes back up to anywhere from 118-128. driving down the road it seems to be holding in the mid 120s. you can smell the exhaust when idling.

O2 seems to be responding fine when cruising. idle is sluggish because of the long tubes. the car has not been converted to a three wire O2, but, like i said, the car was running perfectly fine before the MAF was changed.

Fuel pressure was dropped in an attemp to lean it out. Line on was 48ish and line off was 53ish. it is now at 43ish line on and 50ish line off. this didnt help anything. i was hoping it would change the block learn at least or even the smell. nope.

Purge canister and valves were checked and are good.

plugs are showing signs of running rich, but are fairly new bosch +2s. wires, dist, and coil are all fairly new units.

this is something ive noticed and i think is related but not the main problem the car is having. the car will have zero IAC after it hits closed loop and steadies out after crank up. drop it into gear and it instantly goes to 160. this may be "normal" for this car, but it still feels like its struggling to maintain the idle in gear eventhought it holds at 600 rpm. im thinking that the overly rich condition is causing the full open IAC to keep it from stalling. the IAC is new. the TPS is set to .58. and going down the road the IAC responds to throttle inputs by opening. it eventually goes to zero after holding the throttle steady a little ways. i just found this odd, maybe i havent been paying attention in the past though.

i have not started checking wires and connections yet, that is next. i was hoping maybe someone could point me in a direction though.

now why i have posted all this and arent 100% sure of the direction to go is because the MAF is a good one, the accordian is good and there are no leaks before the TB, and there are none and have never been any codes thrown. if only it had thrown a code to give me some sort of hint. seems simple enough that it would be the MAF, but that is not doing the trick.

any ideas? thanks

 

I just licked a very, very similar problem on my 383 I just installed. I tried everything to get the idle down and not run lean. I found several problems. The first was that the timing, as the motor had broken in and the timing chain stretched, settled in right around 0*. I bumped that to 6* and it ran much, much better. I also replaced the maf relays, both the power and the burnoff ckt one. Then I replaced the maf with a new, not remanufactured one. Those reman ones are garbage and seem to need replacement within 2 months after the warranty gives up on them. This was the third that happened to.

All that and it finally worked out ok. I would ohm out the maf wires from the sensor plug to the computer or ground, depending on where that particular wire goes. Make sure the connection is good at the maf. If necessary, replace the connector with a new pigtail and solder the wires, don't use crimp connectors.

I would swap the maf out with a known good, meaning one off another car that is running well. Any one pulled off the parts store's shelf could've been dropped or otherwise mistreated, or just not fixed right by whoever remanufactured it. And remember, with reman'ed anything, they only fix what's wrong, so while the ckt that crapped out the first time is now good, there's dozens of others that could be 20 years old.

 

thank you. i will check those items as well. I believe, but will have to double check, that the two relays were also replaced.

what are the ohm readings supposed to be or are we just checking continuity? i have an 88 service manual and was just going to go through the 33 and 34 codes diagnostics. I havent looked over it though so i do not know about ohm readings. i also figure the differences between the 88 autos and 89 autos is minimal.

the 87 that the MAF came off is running perfectly fine which is why i grabbed it. so while i know the 87 ran fine i can not say the MAF is absolutly 100% as i have not bench tested the unit

 

Also check for air leaks - spray some WD40 around all the inlet manifold joints etc and watch for white smoke in the exhaust. Air leaks are a primary source of a rich mixture at idle.

 

both relays are supposed to be replaced whenever the maf is replaced.unplug the maf and see if it suddenly runs better.

 

the relays are fairly new. I checked all the wires, circuts, and the MAF and relays yesterday. Everything tested as being fine.

If I unplug the MAF while the car is running the car dies instantly. I haven't tried cranking it without the MAF unplugged. I figure it will do the same thing, not run.

 

oh and double checked for vacuum leaks, there were none as well.

 

How about the injectors? if it cranks and cranks and smells flooded and you floor it and it starts right up, that is pretty much indicating leaky injector(s).

 

Thanks. that was a thought but it was just not possible in this case.

I have figured out what the problem is though. I do not know how this car ran for so long like it did but now its right.

There was no provision on the TB or the UP for the IAC passage. So essentially the IAC worked but did nothing as it went to a dead end. something I am not sure of. the UP on this car is the factory one and there is no passage in it for the IAC. Was the passage in the TB? its an 89. How else could it possibly allow air into the engine behind the blades? The TB is a holley 58mm. I noticed that Holley has two different TBs for these cars 85-88 and 89-92. My thoughts are that this is an 85-88 TB. I feel kinda dumb because I took the TB off the 87 I have sitting around and the Accel UP does not have a passage either. The 87 ran fine really, but its a 4+3 so any in gear loads are backed up with application of the throttle anyway. AC doesnt work on the 87. I never noticed any idle problems with it. So now i have to drill a hole into the UP for it to work right. All I did on the 89 was grind a passage way from the IAC hole into the two throttle bores using a dremel on the backside or gasket side. I also cut away the gasket triangle to help out. this did the trick. Now the car idles in gear great. This proved my original thoughts right. the whole time i was working on this car and scanning it I kept saying to myself its just not getting air somehow, but the IAC is fully open. Now i know what was wrong.

thanks for the help everyone and hopefully no one else will make this mistake also.