michael903

Ok guys i just got a 1985 i-roc z28, it has a tpi 305.When i got the car the fuel pump was wired to a switch on the dash, well turns out the the ecu was not sending 12volts to the relay when the key was turned on. I got a new ecu and that solved the problem, i got the car runing but it did not idle well, i hooked up a snap on scanner to look at the data and all the sensors seem to work like they are supposed to. so i got some propane and shot some under the intake and the idle smoothed up and it ran good.
so i went and got a plentum set for the intake runners installed them and checked the egr valve to see if it was stuck open. I put a new egr gasket and put it back together and i have the same problem. i checked all the vacuum hoses again everything looks good. If someone could help me out that would be great

HF_monster

do a compression check maybe a bad valve, it could also be the heater controls they run off the engine vacuum those might be a long shot but if everything else looks good you never know.

easy check on the heater is if its stuck on the defrost vents its not getting vacuum to the controls.

IROC343

Make sure you used the right gaskets in the right places. Most of these intake sets are universal, they include several gasket combinations, for the early and late TPI setups. It's easy to use the gaskets in the wrong place and create vacuum leaks.

gregretter

I just went through the problems you are having also and I'm still learning. Got alot of help from this forum. What HF_monster said is very true. I went through everything. Still could not get a good vacuum. It wasn't until my valves were adjusted correctly on my newly reconditioned that my vacuum problem was fixed. It actually will throw all sorts of codes if your vacuum isn't good. 15+" of vacuum is what your shooting for. Check your compressions and make sure your valves are adjusted correctly. If your heads and valves are good but just out of adjustment or not good and need reconditioned your valves are not seating correctly. Bad valve seat = low compression which affects vacuum tremendously which throws codes, which makes the engine sound like crap. It's not firing on all cylinders. Just my 2 cents from what little I have learned in my project. Not a professional by no means but want to offer any help I can back for all the help I have rec'd. Good luck.

gregretter

Also, you say you shot propane under the intake. Are you absolutely sure your actual lower intake manifold gasket is sealing?

michael903

the only gasket i didnt replace is the lower

gregretter

If it smoothed out and ran better when you shot propane under the UPPER intake, make sure it wasn't sucking it in at the actual LOWER intake gasket. I would say as long as you got all your upper plenum gaskets installed correctly and ALL the bolts torqued down - Even the hard to get to ones - that it is your lower intake gasket. Do your propane thing again and pay particular attention to when and where you spray that makes the engine run better. It could also be around the bottoms or tops of your injectors. Could be a bad o-ring on an injector not sealing well also. I like to use carb cleaner for the when spraying around the intake. Lots of people say not to use it, BUT, with the little red straw on the nozzle you can point it right where you want it to go making it easier to determine exactly where that leak is.

gregretter

I know the thought of it being the lower intake gasket is frustrating but if it has a sealing issue, it will need to be fixed. Has the engine been apart in any way before you got it? Do you know of any work the PO done to the motor?

gregretter

Once you get NO change in engine sound when doing the spray trick, and you still have the problem, you need to check the compressions on ALL the cylinders.

michael903

ok guys i got the lower intake gaskets put on, it solved my valcuum problem, but the car still runs bad. It has a irratic idle from 1300-650 rpm. Sometimes it dies. Someone one told me that it runs a map sensor or barametric pressure sensor. I looked for one but didnt see it, my car runs a maf sensor, i dont think they run maf and map sensors both??

michael903

oh and for the reccord im geting 15-18 inch lbs of vacuum from 650-1300 rpm

gregretter

Good deal. Now your getting somewhere. Vacuum's good. Mine is MAF also. Are you getting any engine codes and what are they if you are? If yours is MAF, does it run any better or worse when the MAF is unplugged? Also, have you checked and set your TPS and IAC? You can go to the home page on this sight and in the tech articles, there is directions on how to do this.

gregretter

How's plug wires, plugs, rotor and cap condition? How's it run with a little throttle? Smooth or still rough? Or is it just rough at idle?

unprdictable1

iTrader: (2)

I have an 85 TPI Z28 as well. Mine did the same thing for quite some time till I figured it out. What my problem was, was the MAF sensor. I had a code #33. The Maf was not recieving it's 12volt signal from the pcm. Unplugged the MAF and the car ran smooth. In 85 our cars run a MAF Burn unit, it is located right on top of the pcm under the dash on the passenger side. After locating a good wiring diagram and figuring out how it all works, I ran a test by sending my MAF 12volts using a jumper wire. Bingo!! Problem solved. I had a bad MAF Burn Unit. Finding one of these is a task in itself. You local parts store could probably get you one but it's a small fortune!! I got mine from tpipart.net for $150.00, plugged it up and it worked like a charm. The other thing you will want to check (which will not set a code) is the IAC. Plug up a scanner and make sure that it is working by watching the IAC count. Have someone that is experienced in working with diagnoistic scan tools to help you look at all of the data in the datastream to make sure all of the sensors are reading correctly. hope this helps

michael903

ok guys when i give it some gas it runs like a champ, so i ran threw the steps of checkin the iac and tps sensors, it all checks out fine. the maf sensor seems to be doing strange things on the scan tool, kinda hard to tell because the ecm is so slow to update the data on the scan tool. I also tested the burnoff module and it checks out fine. I think im goin to try the maf,