I have several problems.(I also posted this message on the TPI board). I bought an 86 z28, 305 tpi with 143000 miles about a month ago and I have been driving it periodically. It does several strange things.

1)It is difficult to start. I basically have to give it some gas as if it were carb.

2) It freaquently dies when slowing for stop lights. I believe this to be maf sensor related, because when this happens, it will sometimes set a code 33,(sometimes 36) and 45. Also, the idle speed constantly changes. However, sometimes it will die without setting a code. I tried disconecting the MAF and and this seems to have mostly solved that problem. Idle speed is *much* more stable(still changes a little)and it hasn't died in two days of driving this way. Understandably, you can really smell it runing rich.

So replace the MAF possibly the relay?? Is there an easy way to test either??

3) Sometimes when crusing(about 1700-2300 rpm), the car will jerk(not violently), almost as if I were tapping on the accelerator and the RPMs chang slightly yet rapidly. If I take my foot off the gas, it stops, if I step on the gas it stops. So what do you think could cause this? Slipping TC? Bad TPS?

4) It runs rough for a few minutes until it gets warm. Is this normal?

So where would you start trying to fix these things? Also, what general things should i do/check to this car to get it in good working condition?? Thanks for any replies, suggestions, or comments and sorry it was so long:-) ~ Arnold

 

I am having a similar problem with my 90 rs(3.1)....for a few weeks now. When I come to a stop, when ever the idle dropped below 1000 the rpm would drop to 500 then surge to 1000 and back to 500 before stopping at normal idle at 750(or so)...today instead of that happening when ever it dropped below 1000 the car would stall thus i had to put it in neutral and rev the motor above 1000 whenever stopping needless to say i am quite peeved...I checked the vaccum lines with a starter fluid to check for leaks ...while i may have missed a line I found no leaks...i also checked the plenum and intake seams for possible leaks there aswell....while I haven't trouble shot the car today, nothing came up in the past checks maybe it could be the idle air control valve but that was replaced about a year ago*shrug*
any thoughts would be of help
thanks

[This message has been edited by CamaroSpawn (edited January 09, 2001).]

 

REPLACE THAT MAF! Also check and/or replace the MAF relays. Located on the firewall on the driver's side. You also may want to check your coolant temperature sensor. I had a similiar problem and it came down to a bad O2 and CTS but it was only throwing the code for the O2 sometimes. Other times it showed nothing. Hope this helps.
bsa

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"If they do not run, Then they will die." - Stonewall Jackson

'87 IROC, 355 TPI, Converted to SD, 700R4, B&M Megashifter, 3.42, Trick Flow Twisted Wedge Heads, Comp Cam, Comp 1.6 Rockers, Lucas 23# injectors, Edelbrock headers, Flowmaster 3'' exhaust, gutted cat, Mallory coil, Mallory HyFire IV ignition box, Mallory Sidewinder 8mm wires, Autolite platinum plugs, K&N filters, Transgo Performance Shift Kit, Corvette Servo, 2,000 Stall Torque Converter

 

Tomorw I will check out the relays and related wiring. I spent this evening diagosing an empty fuel tank. My car started sputering and dying and stuff. I thought something werid was wrong because it sputterd and coughed all the way home. After 2 hours of playing with it( replaced filter etc) I decided to put some more gas in the tank ( i am the guy with the bad guage, go figure) and it was fixed. I always thought that if it run out of gas, it would just quit like my lawnmower:-). Guess not. Anyway, Thanks for the answeres guys! Arnold.

 

I think I figured out the jerking part. I only seem to experince it around 40 mph and I was reading in the archives that that is where the TCC lockups and sometimes it will lock and unlock which causes the jerking. I will try the test light tomorow.
I have also tried several things with the maf. I tested the wires running between the maf and relays and they all seemed ok. Tapping the maf caused no changed but pushing the connector in (even though it was fully seated) the rpms change it sometimes it stalls. I cleaned the connections and after I put the maf back in and this seemed to fix the problem... for a while. The stalling problem came back after about 12 miles. So what I am thinking is that there is some kind of intermittent short in the maf itself and that handling it makes it start working sometimes. Tomorow I am probably going to order one of the wells units. Thanks for you guys so much for the help. I will keep you posted my progression (or regression:-)). Oh, why is that sometimes the engine stalls with no SES and sometimes SES is on but no engine stalling? I swere car computers are stranger than pc's:-) Later.~ Arnold

 

AB,

Reading your initial post was like a history of a problem I had with my '86 TPI. Let me relate some of my experiences:

First, the hard starting can be caused by a number of things, but generally NOT the MAF. The ECM will pulse the fuel injectors without a MAF signal until the engine reaches 450 RPM;

Second, the stalling at stoplights on decelleration is more likely NOT the MAF, but the IAC stepper motor and TPS;

Third, unless you are getting a constant error code for the MAF or the "tap test" reveals a problem, don't replace tne MAF. If you do replace it, send me your "bad" one please - good MAF sensors are worth about $150.00 on eBay;

Next, slight miss or "chuggle" at low RPM cruise was addressed in a GM TSB on '86 TPI engines. It relates to the fuel map. TCC lockup point, and target idle speeds and the transition between idle fuel (low TPS voltages) and moderate cruise (medium TPS voltages). Read the TSB and see if the problems sound familiar.

Fifth, rough idle until warm is probably NOT the MAF sensor again, but might be an ijector imbalance of ignition problem. My car did this at 22,000 miles and had poor spray patterns from the injectors. A cleaning/flow matching of the injectors solved that problem;

Basically, if you aren't getting a constant MAF error, I would suspect the MAF is O.K. It takes only 600mS of lost MAF signal to set a DTC '34' and 600mS of high flow to set a '33'. Since you are getting a '36' intermittently, I would suspect a problem with the MAF power and burnoff relays. These are about $10.00 each, and are easy to replace. I would start with the MAF power relay, since both the power and burnoff functions rely on this relay to provide a good circuit.

Next, read the TSB on the faulty ("bugged") PROM in the ECM on ALL 1986 TPI engines. Unless you've changed the PROM, the TCC lockup should be at a point of about 28 MPH, not 40 MPH. The factory replacement PROM raises the TCC lockup to 41 MPH, and raises the target idle at all engine temperatures. It also enriches the fuel map at moderate cruise and allows for a wider variety of sensor inputs before setting nuisance error codes, like your '34' and whatever else you might be getting.

If it sounds like I know a little too much about this, it's only because I had the same problems on my '86 TA. It only has 46,000 miles, but had all the same symptoms as your car. Oddly, the problems didn't surface until the car had about 22,000 miles on it, at about eight years of age.

SAve the $200.00 or more on the MAF and check/set the TPS, clean the IAC, set the minimum air/throttle position, and make sure the ignition is in good order. Test cylinder compression and fuel pressure. If the compression is good and relatively balanced, perform a power balance test with the fuel injectors to detect weak, sticking, or plugging injectors.

I'll put a few bucks on the problem being one or more of those instead of the MAF.

For the TSBs, check this site: http://www.nhtsa.dot.gov/cars/proble...ervicemmy1.cfm

For IAC/TPS adjustment, check this files:
IAC/TPS Adjustments.pdf

For help with cleaning/flow-matching fuel injectors, check this site:
Cruisin' Performance

For a MAF power circuit diagram, look here:
MAF Circuit

If you can't find the MAF power and burnoff relays, see this diagram:
Relays

If you need any further resources, just ask.

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Later,
Vader
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