'87 IROC VERT

iTrader: (4)

First, I apologize in advance if I missed anything specific to this topic. I looked around quite a bit before writing this.

My car - '87 Trans Am LB9 (TPI 305) and 700R4.

Engine mods - Holley AFPR and set pressure to about 52 psi on fuel rails. FlowMaster muffler. EGR problem was already occuring when this was done, do I don't think it has anything to do with it. Also recently replaced MAF sensor (due to failure, not to try to solve this problem), cat converter and ECM (but not prom - a friend did this for me, just found out he didn't get a new PROM for me). Everything else on the car is 100% stock. Engine has about 4k miles after professional rebuild to stock specs. This problem was actually occuring before the rebuild.

Issue - Car stumbles and sometimes stalls at partial throttle, and seems to be down on power overall. This is also sometimes accompanied by what I consider to be premature/excessive torque converter lockup which results in things like delaying a downshift when going up a hill and then giving a harsh downshift because the converter seems to still be locked up.

A friend ran a scan on the car (Snap-On scanner) and found what I think was a code 32, EGR. He also told me it was 'flying open too early' and that was causing the problem. He checked the EGR valve with some kind of pump, it worked okay. He replaced the EGR solenoid, that didn't help. So, he disconected the vacuum hose to the EGR valve, and sure enough, the problem went away completely. I left it this was and the car runs great fine now.

I know this is not the real solution. I drive the car 140 miles a day commuting to work, so I would really like to get it running right.

A mechanic I know says my PROM should have 'been changed twice by now' due to two previous recalls by GM. Is this true? If so, could a new PROM resolve this problem? Would some kind of aftermarket, performance PROM be a better bet?

Yes, I know I can buy all the stuff and do it myself - with my work and family stuff I don't have the time to invest to do it right. If I can find an off the shelf chip that will 'mostly' suit my needs, that would be great for now.

Note: I have not changed the TPS sensor. The car idles high sometimes with the EGR connected, but disconnected I don't seem to have the problem. I was thinking of spending the $30 for a new TPS, but I am not sure how to calibrate it correctly so I am not sure if I should do it.

Thank you for reading this long post - I love my car and want to fix it before my wife makes me buy a japanese car to drive to work!

rgarcia63

You may want to check for loose connections, malfunctioning sensors and engine to chassis grounds.
EGR is enabled on/off in the ECM at a percent of TPS when the EGR Temp sensor is grounded, the MAT is above a set temperature, and rpms are =>2000. If the minimum air isn't set correctly the TPS might be out of calibration. See item 8 in the following:

Copyright © 2004 ALLDATA LLC
Idle speed is controlled by the ECM through the Idle Speed Control motor and is not adjustable. The minimum air rate is adjustable as follows.[list=1][*]Ground diagnostic terminal, turn ignition on, but do not start engine.[*]Wait 45 seconds for IAC to fully seat, then with ignition still on disconnect IAC connector. [*]Disconnect the distributor set timing connector. [*]Start engine and allow engine to go into "Closed Loop".
My NOTE: The SES light should be flashing, and should change in frequency when the ECM goes into Closed-Loop [*]Remove ground from diagnostic terminal. [*]Adjust idle speed to specifications using throttle stop screw. [*]Turn ignition off and reconnect IAC connector. [*]Adjust TPS voltage if necessary: With ignition "ON" use a scan tool or 3 jumper wires to adjust TPS sensor to correct voltage specification. Tighten screws, then recheck reading to insure adjustment has not changed. [*]Start engine and check for proper idle operation.[/list=1]
If you still have the problem after doing the above:
You have the wrong ECM because the EPROM doesn't need to be change unless it bad, or you've modified the engine beyond the ECM's ±10% autoranging. You might want to straighten this out before doing anything else. A GM dealer can help you determine the correct EPROM and ECM, or you can have someone verify the EGR enable settings in the EPROM which are programmable, someone may have changed them. The TCC lock-up settings are also programmable.

eric305TPI

It sounds like the valve is getting weak and opening to much to early. I believe Trickster has a flow chart for that code or I can post one tomorrow.

'87 IROC VERT

iTrader: (4)

I think my car is cursed. The check engine light has been on all week, but due to my need to commute 150 miles or so every day, I couldn't deal with it until this weekend. Tonight, I installed a K&N air filter, pulled out of my street and nailed it - it actually did make some difference and I could actually hear the engine breathe. Then, about a minute later, the car started acting like it ran out of gas. Anything more than, say, 20% throttle would cause the engine to just bog and start to die until I let off the throttle. It runs okay at 20% or less. It got me home, and I put it in the garage.

I can't seem to figure out why I keep having so many problems. I just replaced the MAF sensor last week!

Hopefully I can get it to my mechanic and he can scan it for codes - the check engine light is on steady, so something is wrong.

Does this sound familiar to anyone? Could it be the TPS?

Thanks for your advice so far, I will print it out and bring it with me to the Trans Am hospital tomorrow

- Rob

Morley

Forget taking it to someone else to read the codes.
Take you a paper clip and straighten it out, then bend it in a U shape. Pull the cover off of the ALDL (under dash at driver's right knee). Put the paper clip in the upper right 2 holes (pins A&B). Turn the key on but don't start the car. Your fans will start to run and you'll hear some clicking under the hood, this is normal. Watch the check eng light, it will begin to flash starting with code 12...flash......flash..flash, it will do this 3 times then it will flash out any other codes it has stored (3 times for each code). As an example... flash..flash..flash.....flash..flash, code 32.
Once all of the codes have been "flashed" it will go back to code 12, turn the key off and remove the paper clip and put it in your glove box for later use.
Find the meaning of the codes here http://home.earthlink.net/~gellett/diag.htm

'87 IROC VERT

iTrader: (4)

Okay, after much procrastination I dragged myself down to the garage and checked the codes. I got the code 12 as expected, then a code 16 (o2 sensor, I think) as well as a 44 (lean) and a 45 (rich), and I think (I left my notes in the garage) a code 32 (EGR).

So, it would seem to me that a bad o2 sensor would probably account for the odd problems, poor gas mileage and the 44/45 codes. I'll buy a sensor tomorrow and replace it after work. I'll check codes after I replace it and have driven a few miles and see if maybe the o2 sensor caused the car to run poorly and maybe contributed to the EGR oddities.

Thank you for getting me on the right track.

One last thing - after replacing the o2 sensor, do I want to reset the codes? Does anyone know how to do that? I've heard disconnect the battery, some else told me I had to unplug the ECM (which probably gets it's power from the battery, right? so why not the battery in that case?)

You guys seem to know the RIGHT answers, so I ask my fellow third gen guys to set me straight on this one.

Thanks again!

DENN_SHAH

iTrader: (1)

yes, you do need to clear the old codes.
by pulling the fuse you may or may not pull the right 1.
the best way is to unhook the battery for 10 or more seconds with the key off.
after hooking the battery back up & before starting the motor pull the codes to be sure they are cleared.

'87 IROC VERT

iTrader: (4)

I think I am supposed to disconnect the battery when replacing the o2 sensor anyway.

Thanks!

87tpi7749

1st problem; code 32 egr, stumble. The first guy was right, the egr is opening too soon. Why, bad egr. This is a dual pressure egr valve, it only opens when vacuum is supplied & there is a loss of exhaust back pressure. When exhaust back pressure is NOT present it closes a valve inside the egr & allows vacuum to pull it open. That is why with the engine off the valve opens. However the valve should not open with the same vacuum applied & the engine running. When the egr opens before it should, you get the stumble. With the mileage you have on the engine, the egr passage is no doubt carboned over & is causing the valve to open prematurely. Replacing the valve fixes this problem. So test it. Apply vacuum to valve with engine off-valve should open. Apply vacuum to valve with engine idling-valve should NOT open. If it does, replace it with a new one (not used) I can only recommed o.e. for flow accuracy & fit.

2nd problem;clear codes & recheck. Sounds like you may have disturbed the MAF connector when servicing the air cleaner, check to make sure the air intake boot is installed properly, it's easy to miss under the throttle body.