5sfe computer bad??? Options

[Marsstar505]

I have a 94gt and I have replaced the iac valve 3 times with new ones oem and it still won't idle right. At first when I swapped it it was perfect 750 rpm idle then after about a month it started to fluctuate then it got worse and wouldn't idle at al and would just kill the engine till warm. I tested the voltage at the ecu with the engine off key on and one wire to the iac had battery voltage and the other had .23 volts my pin out chart says it should have battery voltage at both. Also when driving I occationally get fuel cut at 4000 rpm and it's hard to get it above that. I'm thinking it's the ecu but I'm not sure. Any ideas are helpful.

[Smaay]

if you are getting some sort of shutdown at 4000, check your timing. I have seen this before and it was caused be the timing belt slipping a tooth.

[Marsstar505]

The timing belt only has 10k miles on it. It feels like when you get fuel cut for max rpm. It only cuts once then let's me rev more but it is ruff for the rest of the rpm range. I'm sure the timing belt it right on but I did advance the distributor timing to 14 degrees could that cause it. Also on cold start up it has a random miss fire and shoots raw fuel out the tail pipe.

[HaysoosKreesto]

Sounds to me like a type of leak, when was the last time you replaced any of the hosing? After 20 years of use they may get worn down.

Also, I am not anywhere near the level of knowledge that some members have here, I can only help guide you to what possibly could be wrong. One thing I've noticed with Japanese cars in particular is, when something is wrong it is typically a worn part that is normal for replacing is due for replacement. Perhaps when they put on the new timing belt they rushed it and didn't correct the timing?

Maybe the fuel pump has gone the way of the do-do?

Maybe it's not breathing or exhaling correctly?

I'm about 90% sure it has to be a leak SOMEWHERE, problem is where the heck to look?

[VavAlephVav]

You can take the ECU out and carefully inspect the circuit board with a flashlight. If you see any burn marks or goop coming out of the capacitors.
Usually if its bad you can visibly see it on the board. But not always.

[Marsstar505]

I rebuilt the motor 10k miles ago and at that time I replaced all hoses including coolant and vacuum. That is also when I changed the timing belt my self. I had the oil pump seal start leaking and I had to change that and the timing belt was redone. The problem has existited before and after that. And I will pull the ecu and check it.

[mkernz22]

You should try retarding the timing. 14 is a little much...

[VavAlephVav]

I think stock ignition timing is 12 degrees if you've got an odb1

[Marsstar505]

There is a small spot on the ecu but it doesn't look like it burned through the wires. It connects the main chip with a sub chip. And I can try adjusting the time back the factory is 10 I set it at 14 because I was told that is a safe advance for the 5sfe and it increased power and response by a lot.

[Smaay]

14 is safe, but you should be running premium gas. your knock sensor might be sensing detonation and retarding the timing

[Marsstar505]

I retarded the timing back to 12 degrees and now it is very smooth on power it got rid of the surges and it doesn't hold back randomly now. But I still have very random fuel cut at 4k and the idle isn't right still.

[Marsstar505]

Can anyone confirm that the pin voltage chart is right and that pins 9 and 10 on the 22pin connecter has battery voltage with the key on engine off in a car with a good idle?

[bboytech]

I think that those IAC valves rarely go bad,as long as you keep them clean.My car (94 gt) was fluctuating on idle badly and wouldn't start after heating up and the problem was the coolant temp sensor,I replaced it and everything normalized.My IAC valve is original.You can disconnect the sensor to see if theres a change.( it's the two wire sensor)

[Marsstar505]

I replaced the coolant temp sensor as it was cheap. And I readjusted the tps sensor and it still do was the same thing. If I plug in my iac it closes the iac and almost stalls out, and unplugged it idles a little up and down.