I have just finished converting my 87z from a 2.8 to a 3.1, the problem is that the car will idle rough, then, all by its self, the idle will climb up to roughly 2500-3000 rpms, then suddenly drop off and die. But then it starts back up and will idle fine for a while??? I'm lost. The car ran fine with the 2.8, other than a rod was going out. Also does anyone know where the temp swich is on a 3.1? Not a clue, I juess i can look at a Berretta since that is where the 3.1 came from.

It sounds like either a vacuum leak or an issue with the ECU.

Symptoms of a vacuum leak are rough idle, stalling, and high idle. Check all your vacuum hoses and make sure everything is connected, and make sure that there are no unused hoses on the new engine dangling in the breeze.

From your description though, it sounds more like an electronics problem. Throttle Position Sensor to be exact. My friend had an 88 Toyota 4Runner, and it used to do practically the same thing. It would idle way to low, then the RPM's would surge up to about 2500, then down again, then back up to 3000, then down to 400, ect. After it was started and driven and then restarted though, it would usually be fine for a while. We took it to Toyota to get the codes pulled, and they came up with the TPS code. The guy adjusted the TPS back into calibration, but it was well worn out and really needed to be replaced.

So check out both those options and see what you come up with, good luck.





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I agree a code check would be a MUST.But with irractic idle would point specifically to the TPS.U can do a simple check with a multimeter to varify,but I am not going to go into to all that.I can share a web site that will tho http://www.wellsmfg.corp.com click on diagnostics volume 2 issue 1.This has a step by step process of checking ur tps,basically if the resistance goes up or down REALLY fast and not gradually the tps is SHOT.I hope this is somewhat usefull I have gained alot of info thru there site,on electronic issues and such.

Well, to answer this issue , i called over a friend that is ASE certified, his suggestion,
a vacume leak... On the 3.1, on the bottom of the intake plenum, there is an extra vacume line, I had it plugged into the back vavle cover, and the correct vacume line, the one coming out of the intake pan, was just left open. I plugged off the wrong one and fixed the right one and , wahlah, problem fixed. But now, the new problem.
Now the car has a sever studder, I can give gas and it sounds like it losses power, and wants to die, and in fact does. But if i ease on the gas it will go, but i have to feather the throttle. Any Ideas??

check that the vac lines on the top of the throtal body are corect
one line goes from throtal body to fuel pres reg then to the map sensor
other small line goes to heater controll and vac resovare
the larger one goes to charcal canister
the port under the plenum goes to the pcv
large port on side of intake goes to brakes

if all are good suspect posabull coil / coils braking down

what ecm and prom are you running

I'd also consider the TPS--they're inexpensive and easy to replace.


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