gresmi

Good morning everyone,


I had a frustrating night last night. I have been fighting my '86 305TPI now for months and I can't seem to make any headway. I have been reading hundreds of threads trying to find the same symptoms. I keep thinking i'm getting close or i'm onto a solution but nothing has worked so far.


Symptoms:
Car usually starts and idles fine. When warmed up car idles around 750 RPM. When the electric fan kicks on, while idling, the car wants to die as the RPM momentarily drops to around 450 RPM. It will flash check engine light and then quickly rpm will raise to around 600 RPM and when the fan turns off it returns to 750 RPM. The car will sit there for 20 minutes and idle, no problems other than what I indicated above. If I turn on the AC the RPM adjust correctly, increasing slightly to compensate for the load. But, when I put the car into reverse and drive just a few hundred feet, the car's rpm's drop to 450-500 and the car is barely running. I then switch to park, without a change in RPM, and drive maybe a few hundred feet. Shift from 1st to 2nd with slow acceleration...then when I let off the gas to coast the car immediately dies. I can replicate the problem 5-6 attempts but sometimes the car will stay running but just barely.


What I've tried so far:
Diagnostics check/test didn't work, it couldn't connect to the ECU. Thought maybe the computer was bad. Slap test on the ECU. The car died, bought a new ECU replaced the board with my existing board. No change, if anything the car ran worse. Put old ECU back in.


Checked for vacuum leaks, couldn't find anything.


Pulled the IAC and cleaned it with carb cleaner, put it back in (I did not recalibrate it). No change


Adjusted the TPS in both directions from where it was originally set.


I do believe the car is running slightly better than before. Since cleaning the IAC I don't seem to be having any back fire issues. But, the car seems to switch from running 'normal' to 'retarded'. And when I say retarded, I mean it just isn't as responsive, it doesn't want to idle, it doesn't like to start as easily. It is like something is just switching.


I just don't know what to do next. The only thing I can think of is replacing the IAC with a new one. The car has 40,000 miles on it and i'm assuming it is the original IAC but I don't know for sure. I'm also thinking maybe I bought a crappy ECU. It didn't cost a lot, like $89 or something.


Other things i'm considering to do to the car, not in any particular order:
New EGR
New TPS
Start replacing vacuum hoses that look old
New O2 sensor
New rotor/cap (I replaced once already a few years ago)
New MAF. This one is low on the list simply because of how sporadic the problem is.


Any help or direction would be greatly appreciated as i'm at a loss.


Thanks in advance to anyone that has made it this far through my thread!!


Greg

thtanner

iTrader: (1)

You say you think the next step is to replace the IAC, but you haven't even done the reset procedure on the one you have. I'd take smaller steps, personally, and maybe do the IAC reset. It's pretty simple. Not sure it's your cause but hey, replacing something you haven't even 'calibrated' yet seems silly.

gresmi

Thtanner,


That is a good point, I did not do that. I just cleaned the old one and put it back in. I thought you only had to recalibrate a new IAC, guess I didn't pick up in all my reading you should do it to an old one. I will try doing that tomorrow night.


Thanks for the input, and I agree to test the old before buying new. I already wasted money on the ECU, still upset about that!!


Thanks again,


Greg

Vader

With a 1986 305 TPI, how does one "calibrate" the IAC?

zero13

....or any year?..Never heard of that myself...I just removed mine when I blasted my intake and put it back in( it was recently replaced)...

Camaro86IrocZ

iTrader: (1)

I always thought it was this -

thtanner

iTrader: (1)

It's more commonly referred to a reset - you may have heard that term more often.

Hawkeye1980

iTrader: (3)

Hi,

Been fighting will all sorts of codes and starting/running issues myself. Did you try this?


I JUST did this and now the car runs amazing! No codes, idles perfectly, starts right up.

I put in a high performance starter last year, and all my code troubles seem to have started at the same time. . I did the following:

Last Summer:
Replace IAC
Replace TPS
Replace EGR
Replace all vacuum hoses
New set of gaskets for plenum last year, had to scrape them off
new South Bay fuel injectors
No good, was getting codes, 22 and 42 mostly, gave up

Just this past 2 weeks:
New wire from ebay that connects to EGR from Vett.
new gaskets again for plenum and runners, used some RTV because I scraped them last time, worried about vacuum leaks
Started her up, check engine light on, idle very high, around 2000RPM steady, getting only code 22 now
Adjust IAC as per video you posted above, found it on youtube as well. Now car starts, but dies immediately
adjust the TPS just 30 minutes ago, NO CODES, car runs perfectly!

Hope this helps!

gresmi

UPDATE:

I think i'm getting closer. I appreciate the responses over the weekend and I think I did everything reviewed in the two videos. I used the procedure to reset the IAC from this forum which was a lot more difficult than what was described in the above video. I put a jumper on A/B terminals from the ALDL to go into diagnostics mode, ran the car, etc. This was difficult as I couldn't get my car to idle at 400 RPM, it was closer to 450 RPM. Anyway, did all that, adjusted the TPS to 0.54V, then drove the car. This was Saturday and we drove the car for 30 minutes without any issue. I thought I had this thing fixed, even to the point I was looking forward to coming to work to tell everyone what I did to fix it!! One other thing we did, the car was running fine and I wanted to get rid of the CEL so I unhooked the battery for a few minutes and started the car again. I thought the car started a little hard, considering it was warmed up, but it started and seem to idle fine, no CEL light, thought I had it. Then Sunday rolled around and we drove the car. It went maybe 5 minutes and died as rolling to a stop. Crap. Drove it some more and it died again. Maybe, in total driving time of 30 minutes, it died three times. I feel like i'm getting close to the problem as this is still much better than it was preforming in the past but still makes no sense. I drove it to work today, 25 minutes highway driving, and it died once as I was leaving town. I'm, again, at a loss.


I figured tonight I would try resetting the IAC again and recheck the TPS. That is all I know how to do. Does anyone understand why the procedure in the video is different than the procedure described in the sticky here in the forum? To be honest, neither make much sense to me.


I do have a question, when I put the new IAC in should I manually turn the pin in some? When I pulled the old IAC out the pin was frozen, I think the pin had seized against the guide. I forced it to turn and it broke the plastic guide inside the IAC housing. The new IAC appeared to be almost fully extended. I'm wondering if I should take the IAC out and manually turn the pin in slightly to ensure when I screw the IAC back into the manifold it is correctly seated. This may explain why it ran so good on Saturday and ran differently on Sunday??


Any help/advice would be greatly appreciated.


Greg

thtanner

iTrader: (1)

Just install the IAC and perform the reset. You do not spin anything prior to installation.

gresmi

UPDATE 2


Drove the car home from work last night and it ran great. No stall issues, no hesitation issues, started up fine, no check engine light...it seemed normal.


Given the car ran great I didn't do much to the car. I did recheck the TPS voltage, it was at 0.58v so I readjusted it to 0.54v but that is all I did. Figured I would drive the car again today and the fun started again. The car started sluggish, I mean, it didn't just fire right up to 1400 rpm or even a high idle...it turned over a few seconds then idled at 500 RPM, barely. I let it sit for a few seconds to see if it would clean up and it never did until I applied a little throttle input, then it went up to 650 RPM, still too low for a cold engine. On top of that, I was getting a CEL flashing on and off, sometimes staying on for a few seconds, very sporadic. Drove the car to work which consists of about 5 minutes in town driving and 10 minutes of interstate (80mph). The car seemed Ok and didn't stall once. Pulled into the parking light and the car seemed sluggish with throttle input and the CEL started flashing again. When I gave the car throttle, say to 2000 RPM, it rev'd a little sluggish and when I let off the throttle the car would act like it was going to die, falling immediately to 500 RPM but then pick back up to 600 RPM and idle Ok.


I'm not sure where to look now. ECM? Vacuum leak? Crappy new IAC? MAF? I know I've made a change, last week the car wouldn't have made it to work without stalling a half dozen or so times and today it didn't stall once. I should note, I replaced the old IAC with a BWD brand from O'Reilly's. I know, its not ACDelco but they had one in stock Saturday so I bought it. I hope that wasn't part of my problem.


All for now, we'll see how the ride home is tonight.


Greg

Camaro86IrocZ

iTrader: (1)

This may be unrelated, but Vader posted this years ago and it helped me, Seeing that you have a 1986 it's worth a look -- http://www.gmtips.com/3rd-degree/dox/tips/ecm/prom.htm Solved my check engine light problem as I had one of the proms listed.. My car runs way better with the updated chip... I wonder how many of these cars are still going today with unknowing frustrated owners, I always had a hunch, this TSB just confirmed it.. I know it says firebirds, but camaros had em too..

gresmi

Thank you for the information, I had no idea this TSB was out there. And yes, my car suffers from all of the above symptoms. The shutter/jerking 1 to 2 shift being the most annoying. I'm anxious to pull my ECM out to check the PROM. I have already sent the bulletin to my GM guy to see if he can still order the PROM.


Thanks again!! I don't believe this will solve my stalling problem but if it helps with the torque converter lockup i'll be very happy!!


Greg

Camaro86IrocZ

iTrader: (1)

You can swap any of the newer chips as well, up to '89 I believe. Just make sure it matches your setup, LB9, auto or manual, rear gear ratio, tire size,
ect.. I got lucky and found a oem 1228291 on ebay years ago..

gresmi

That is good to know. I'm hoping to pull the ECM tonight or tomorrow night.


Thanks!!

gresmi

UPDATE #3


Another frustrating morning driving the car to work. This morning, the car ran great for the first 15 minutes then, as I coasted to a stop from the interstate off ramp...it died. Car started right up and didn't die again. At lunch today, the car started right up...CEL light flashed...RPM dropped to 500'ish...then it died. I started it, without any throttle input, it barely started and idled around 500 RPM for a few seconds and it died. Started it a 3rd time, same as the 2nd time and died. Fourth attempt the car wouldn't start...cranked for a few seconds, turned off the key, tried again...I did this maybe 5 times and it finally started. Once it started, no CEL and the car ran fine.


My plan is to change the ECM tonight. While doing that i'll check the PROM to see if it is original.


I really thought I was making some headway. I know the things I've done have improved how the car runs but today it acted more like it did before the new IAC. Frustrating!!


Greg

Camaro86IrocZ

iTrader: (1)

Thinking on it, back quite a few years ago, I had a similar problem, took it to the dealer who had a tech who knew these cars and the common problems of the day, he changed a fuseable link or relay if I remember correctly, it was the early 90's so my recollection may be off.. I remember it being very frustrating at the time.. Once you get all the little quirks out of the way, they do run nicely. I haven't really had major issue's since..

gresmi

Thanks for the reply and I'm sure i'll finally stumble upon it and it will be something simple. I thought I had it when I replaced the IAC. We have had this car now for 4 years now and, until this happened, it was a very reliable car.


As sporadic as the problem is now I'm wondering if it isn't the ECM. That is the next thing to try, hopefully tonight.


Greg

gresmi

UPDATE #4


Good morning everyone. I put the new computer in last night, ran the car for 20+ minutes, and it ran fine. No check engine light and it seemed to idle pretty good. If anything, I thought the idle while in gear was a little low (500 RPM) but it never stalled.


I did look at the PROM manufacture date, it was the 39th week of 1985. Which doesn't surprise me after reading the TSB sent to me last week. My car suffers from all of the listed symptoms listed in this TSB so my next quest will be to find an updated PROM. http://www.gmtips.com/3rd-degree/dox/tips/ecm/prom.htm


Verdict is still out if the ECM actually fixes my problem. At this point I'm not convinced yet but hopeful it does the trick.


Thanks again for everyone that has offered advice.


Greg

crazymex83

You mentioned that once the electric fan would kick on then troubles started. My first thought was a bad ground. I would have suggested adding some grounding straps to your engine and battery. I remember cars having electrical issues when the grounds would corrode and all the guys I used to work with did was to grind off the rusty areas, reattach the grounds with some gunk that protected against corrosion.

I'm glad you got results with the ECM/PROM. I hadn't heard of that but my car is an 88. You did also mention the EGR. I assume the vacuum line and any electrical connections are connected. My engine had the vacuum disconnected somehow and after fixing that my gas mileage went up too.

gresmi

Thanks for the response craxymex. I don't believe the fan and/or ground has anything to do with the problem, it was just an observation...and observation I found strange. The ECM/PROM, I believe, is an issue that I will address next. I'm still running my original PROM with a new ECM now.


Greg

gresmi

UPDATE #5


I think I might have solved the stalling issue but time will tell. It has been over a week since I've installed the new ECM and the car hasn't stalled yet. Not sure why this didn't fix it the first time I installed the new ECM? I did start with a new ECM and I thought the car ran worse, if I remember correctly, the car wouldn't even start with the new ECM so I took it out. I then found I had a bad IAC valve, replaced it and I thought the car ran better but still would die. Two weeks ago now I put the new ECM back in with the original '85 PROM. It seems to be running good but we haven't driven the car all that much.


Thanks again to everyone that offered opinions/suggestions, they were all very much appreciated. This one has been a head scratcher for sure!!


Greg

ikeepitreelz

"

Curious, any Update #6?