1st post new to the board

David is my 16 year old son who got an 87 IROC TPI for his birthday. I knew it had some issues but he really liked the car and it just passed CA smog. I dont know how it passed. It is supposed to be a 5.7 that replaced a 5.0 but still has the 5.0 PROM.

The previous owner put alot of new parts in it fuel pump, injectors, MAF (aftermarket), relays, EGR, O2 sensor, IAC, dist cap, rotor, plugs, plug wires, cat.

Along with that for some reason many of the wires have been replaced in the engine harness mostly going to the MAF and ECU and the relays. The PO said this was because of a short and the wiring pin to pin is original. He also put in a 160 degree thermostat and rewired it so the radiator fan is always on.

Scanned with Winaldl and attached datalog just running engine in the driveway. Codes 32, 33, 34, and 36 are on. I printed the troubleshooting steps for these but have not done it yet.

The car has an intermittant problem where it stumbles and idles up and down. Happens once a week or so. It has gotten better since I cleaned the throttle body. Vacuum gauge is around 18. The IAC on the datalog is high and the exhaust smells rich

Tonite i tried setting the idle with the procedure on the technical board. Installed short between ALDL A and B turned on ignition and removed IAC connector after 30 secs. Started but unable to get the RPMs below 1200. The idle screw was not in contact with the throttle. My first thought is vacuum leak or possibly a mechanical issue with the throttle. When I put the IAC connector back the idle went to ~800. Any thoughts on this would be helpful.

With all that the car runs pretty good

 

It sounds like you did the idle setting procedure wrong. Your IAC needs to be full seated (closed) when you set the minimum air rate.
When you plugged it back in it had to close more in order to lower the idle speed back down. Obviously it wasn't fully closed before.

 

Make sure you verify the timing before setting the IAC and TPS... had a hunting idle and rich smell on mine, no amount of adjustments could fix it, found the timing was retarded and now it runs like a champ.

 

Would like to time it correctly but cant find the tan/black wire with a cap on it. Where does that tan/black wire come from? Someone made a mess out of the wiring. I put the timing light on it and it was ~6 to 8 *BTDC. Kind of hard to get the light in there. I am going to have to start looking for an engine harness.

There is an open connector near the distributor that does not seem to have a place to go. If it looks like the fuel pump connector then the PO may have wired the new one differently.

Going to look at the throttle body to see if it is closing all the way and pull out the IAC to see if it is also closing.

 

It looks like this:
http://tpiparts.net/inc/sdetail/774



Try looking on the passenger side near the cowl area above the A/C box.

 

Unplug the MAF meter and start it up. Sounds like the MAF is shot.

 

Next verify that block is a 350. If you still have the 305 prom with those 350 injectors and knock sensor ,it won't run very well anyway.Get a flashlight and look at the block casting. It is located behind the driver's side head on the block near the bellhousing. It is there,trust me. Next , if it is a 350, verify you have the correct inj. AND KNOCK SENSOR. Then , if you do, the easiest and cheapest thing to do since you already have a 160 degree thermostat,would be to buy a used hypertech thermomaster prom. Also,that fan will not last running all the time like that.

 

EST is a brown wire with a black stripe. It comes out of the big black, plastic harness cover near your ac/ blower fan.

 

What a coincidence! My name is David and I have an 87 Iroc that also has the surging idle and rich smelling exhaust. I dont have any advice (I still have the same problems so I obviously dont have any advice) but I will subscribe. I agree your MAF could have gone bad (those aftermarket ones arent any good). I got new plugs and O2 sensor about to go in but the MAF will be getting fixed soon too. May I ask what brand of MAF sensor did you buy? That might help us to recommend a different sensor for you if that is the problem.

 

He ought to just unplug it and see if it runs better. Then he will know for sure.

 

Ok.. removed the throttle body and the IAC and noticed a lot of carbon on the hole the IAC needs to close. Cleaned it with carb cleaner and cleaned the other side of the throttle body. Put it back together and it started and died. Adjusted the throttle up and it started idling smoothly. I think the new IAC was not closing completly due to the carbon buildup so the throttle was completly closed and it still ran. Need to scan again and see if the IAC number went down. Also installed a new TPS and set it to 0.5v.

Thanks for the help on the brown/black wire.. it was on top of the AC. Checked timing and it looks like 6*BTDC with the connector unplugged.

Unplugged the MAF and the SES light came on and it idled high around 1500.

David, you may want to remove the throttle body, clean it, remove the IAC and clean the inside where it closes with carb cleaner and a rag.

 

What codes do you have now?

 

So what is the first pic of and what is the second pic of? Do I have to remove the thing in the second pic to clean it because I have seen a video on youtube where they cleaned it and it was still on the engine. Where is the thing in the first pic located?

 

Look on the other side of the engine compartment:

 

You can clean the throttle body without removing it but may not get the backside very well. The pic on the left is the IAC valve located on the lower pass side of the throttle body. You may be able to remove it and clean the inside on the car but I thought it was easier to take it out. The water connects have been bypassed so that made it even easier.

 

Do you have a picture of where the IAC is on the engine? Also is there anything to disconnect while I clean it on the car?

 

You may want to get a Haynes or Chilton manual for 20 bucks, Ebay has service manuals on CD's for 30 bucks, or find a good mechanic. There are lots of sensors on the engine, IAC, TPS, 02, MAF, temp.... and these manuals tell you where they are located and how to test them.

 

Dang I forgot all about my Chilton manual! I guess I will try and find it in there. Thanks for the suggestion!

 

Still working on the intermittant running rough issue. It was showing code 42 EST so I replaced the knock sensor and the electronic box on the firewall. It dosent knock but the rough run seems like its trying to retard the timing. Sometimes it goes away in a few seconds but if it lasts you have to turn it off and restart. The sensor didnt fix it so I unplugged the tan and black wire that goes to the distributer. Noticed when I was setting the timing it ran really good and has not run rough for a week with the wire disconnected. I was thinking it may be the ECM. That is an $$$ item. Any ideas on how to test the ECM to see if the EST circuit is bad?

 

code 42 comes on when you unplug EST. Knock sensor is code 43. Still sounds like an ecm issue to me. Well, at least you can count those 2 items you relaced out. I would ohm your injectors too. If you cant pull codes/ no CEL ,then you probably still have a bad ecm or wiring.

 

Sorry , i sent you the attachment for a 7730 ecm,forgot you had a 165. Check this link https://www.thirdgen.org/forums/v6/4...m-pinouts.html

looks like d4 and d5 are est. You can use the ground from the aldl with it. looks like with engine running est bypass(D5) should be at 4.75 V

 

There's a possibility that your distributor is worn out. Have you checked it for slop?

 

Hey 91 thanks for the help.. Guess I changed out the knock sensor for no reason. I will trace out the EST wire. I looked back at an old ALDL and it was showing code 42 with the tan/black connector plugged in.

305sb - I replaced the dist cap, rotor, module, and coil. When I had it out it seemed pretty tight.

Will get back after I buzz out the EST wire.

 

Ninety one was right it was the MAF. Replaced it last week and it has not glitched since. Thanks for the help