I did a major tune up in hopes of passing smog. I failed the idle portion of the test due to high HC's 220 ppm is the limit I ran over 700 ppm. During the tune up I found a few vac leaks and fixed them. After this it ran much better. A few days later the car started to develop a part throttle buck under light load, (high gear, pulling a hill, part throttle) It is not a constant it only happens about 50% of the time Also at a light, I get an occasinal rough idle. This only happens after the car is fully warmed up. When I first start the car it runs and idles GREAT. The SES light does not come on when the car acts up. The only time it comes on is on the interstate at a constant load, constant throttle for an extended time, (more than a min. or so) I pulled the codes tonight. I got 23,32,33,43,45. My cheap Haynes manual show them all pointing to a bad ECM. I got these by jumping the ALDL pins A and B. I will verify these with my Snap-On scanner at work on monday. I'm looking for bad wiring ot somthing else obvious. My car is an 1988 with the 305 TBI Vin E engine. The only modification to the car is a manual fan switch The temp NEVER climbs over 200*F. Any ideas, I drive this car ever day and I really like it, but if I cant get it to pass smog I will have to get rid of it. I have put a ton of new parts in it (suspension, brakes,rad, rebuilt the tranny and stereo) and getting rid of it would SUCK as I always wanted one in high school and now I have it! PLEASE HELP IF YOU CAN. I will do any testing that you ask me to (I have the tools but am not that familar with engines( I do trannys for a living) Keith

 

Before replacing parts, I'd do a little trouble shooting. I think you have multiple problems going on and I doubt its the ECM.
Did you reset the codes after you fixed your vacuum leaks? If not do so before you start trouble shooting and come back and let us know what codes it gives you. Always reset your codes after a repair.

Start with your code 23. This indicates a bad air temp sensor or an open in the circuit.
Check the sensor. Is it plugged in?
This sensor is a variable resistor. With the wires unplugged from the sensor take an OHM reading of the sensor with your multi-meter. If its above freezing out and the ohm reading is above 40,000 ohms, replace the sensor.
You can do a continuity check on the wires with a multi-meter when they are unplugged from the ECM and the sensor... is there an open? If so, find the open and repair it.


Other stuff to check:
What is your manifold vacuum when its warmed up at idle?
Is your timing set properly?
Check to make sure you hooked all your plug wires properly.
Check plug wire condition, none burned through on headers or cracked or chaifed through.
How did you do your manual fan switch? Did you use the wire from the sensor in the passanger side head and hook it up to a switch to ground? If I recall its a brown and white wire.
Have you installed an open element air cleaner?


Let us know if you find anything and we can move on to your other codes.

 

I'm going to clear the codes and go for a long drive to day and see what codes reset. I'm troublesooting the idividual componets today. As for the timing The hood was replaced before I bought the car so I do NOT have a VECI lable. I will check it today and report back with a vaccum reading. The fan switch (again done before I bought the car) is a simple circuit. power from the bat. through a fuse (40amp) to a relay to the fan. the relay is controled by a toggle switch under the dash. the air cleaner is a stock Fram replacement. I'll be posting again later today. Keith

 

OK I checked the timing. With the ESC in bypass it is set at 0*. My gauge shows 20" at idle (reading taken straight from manifold) I cleared the codes by disconnecting the neg. battery cable and connecting it to the pos. cable and letting it sit for about 3 hrs. I checked for codes they were clear so I started it up. (before I had to depress the gas pedal a bit to get it to fire. Not now) I let it get up to operating temp and went for a drive it ran pretty good. I got a bit of ping on an uphill grade in 4th gear at low speeds with the TCC on. If I shift to 3rd the ping is gone. The tank is full of 87 octane. The idle is pretty smooth ( for a motor with 187K on it) On part throttle accell there still was a slight miss on a hunch I shut the fans down and let the temp go up to 220*F After SEVERAL attempts to get ping I could not. I tried to get the SES to come on by cruiseing at steady throttle for a while but traffic got in the way. There is a good place for me to re-create this on my way home from work will try on Monday. I'll keep you posted. Keith

 

When you reset the ecm it has to relearn your driving habits. It takes 20 to 30 miles of driving to do this.

Steve

 

Well as luck would have it the SES light came on during the drive home today. the same symtoms intermittent rough idle bucking on accel. ect. the codes stored are 32 and 42 I will look them up after dinner i think 42 ie ESC and 32 is EGR related Any hints on were to begin?? Keith

 

187K miles. EGR maybe be pluged up a bit, try physically moving the valve by pushing up from underneath it(just to break it loose). I'm also a fan of those fuel system cleaners. If the engine is full of carbon deposits from someone else not driving the car(grandma)/taking care of it, maybe that's causing the pinging. One of those fuel system cleaners will help that IMO. These cars have no timing advance in them, so they shouldn't ping at all with the timing set at the stock 0* setting. I mean somewhere ~20-22* at WOT and maybe 26-30* at mid rpm cruise with the stock chip and dist. set at 0*.

I bet a new cat would help mask you emissions problems also, just a suggestion.

 

The EGR valve moves freely I'm not sure if it is sealing I'll pick of some cleaner today any particular brands I should get? I'm looking into a cat now. Keith

 

I don't know which kind is best, I know Lucas makes one that pretty cheap ~$3. Any of the complete fuel system cleaners.

 

I'll be needing gas tomorrow (If I drive the iroc) I plan on filling up with 89 octane and 2 bottles of top engine clean. I'm more concerend with the drivability issue. If all I wanted was an emissions stamp, thats a problem that a $50 bill will take care of. Keith

 

I had to run 91 octane with my 305 tbi 5 speed. Because of it's age and mileage 200,000 km. 120,000 miles, the timing chain was stretched out giving bad timing. I was told by several mechanics to change it. Instead I put a 350 with a mild cam in. Now it hauls *** and is emmisions legal .(Can't visually tell it's a 350)