Slow Start & Rough Idle. No Clue!?

[travs_dsm]

1997 Eclipse GSX Automatic
67,000 miles
100% Stock no mods

Parts replaced so far:

Coolant Temp Sensor
Gas Cap
Plug Wires
New battery

Tests done so far:

Tested ISC, got 33ish Ohms across all leads

Background:

The car was overheated (busted turbo coolant hose) and required a new head/head gasket. I'm not sure if the car was hard to start before as it did not have but 14psi across all cylinders when i got it.

So the car takes forever to crank when cold, although me giving it gas via the pedal seems to help it finally start. It will never start if I just turn the ignition without pressing the gas. Once the car cranks, it has a rough idle: 750RPM in Neutral all accessories off per spec. In gear it drops down to like 400RPM and the idle of course gets very rough. I am not getting any CEL and there are no codes in stored.

The car runs great other than the rough idle and slow start. Also when I am cranking it for a while I can smell a ton of fuel which led me to replace the Coolant Temp Sensor just in case, but it made no difference. Another possible clue is that warm starts are much easier than cold.

I have replaced the battery (800CCA), NGK plug wires, CTS and even the gas cap. I was sure it was the ISC, but it tested out good with the multimeter.

I'm at a loss and I don't know what else it could be. I'd appreciate any help offered in tracking this down! Once I get it running 100% I'll post some pics of this thing, it is gorgeous! Thank you!

 

[92AWDHX40]

Terry's Talon Troubleshooting Tips #3 - Fast Idle (aka. Idle Surge)

idle problems, check your coolant temp sensor too.

 

[travs_dsm]

The idle isn't surging at all though. Once it starts it idles in place, just rough.

Interestingly, if I disconnect the Coolant Temperature Sensor (which I just replaced new) the car fires right up. Of course it trips the CEL shortly after when it is disconnected.

New Coolant Temp Sensor is testing bad. I'm going to get a new one and see if that works. Will update.

 

[92AWDHX40]

Sounds good, the idle thread is always helpful with small things i had idle issues not fun.

 

[DannyHart]

Tune issue ## probly getting to much fule at an idle that would explane why you can startup without the coolant temp sensor easly.

 

[travs_dsm]

So I replaced the Coolant Temperature Sensor again, but it didn't fix the issue. Same thing: slow crank when cold, but starts if I give it gas OR disconnect the Coolant Temperature Sensor. I'm at a loss

 

[travs_dsm]

Pulled the plugs and replaced them with some new NGKs. No luck.

One thing I remember, is that when I first put the car back together it threw a Idle Air Motor/ISC code, think it was P0505. Since then I tested resistance across the coils it they all tested good. I haven't gotten the code again since clearing it. Could it possibly be bad, but not testing bad on the multimeter? Should I take it into Mitsubishi to have them adjust the BISS correctly?

 

[BWeston]

You're experiencing a spark issue. Check your coil pack and power transistor, one of them is probably bad.

 

[travs_dsm]

Thanks, I will check the coil pack and resistor hopefully today when I get home from work. I'm also picking up some carb cleaner on the way to test for vacuum leaks, although my buddy is telling me a vacuum leak wouldn't make the car hard to start? I have my doubts !

I'll be sure and update this thread as I go along so it may possibly help someone else experiencing the same thing later on down the road.

 

[92AWDHX40]

How about, the throttle position sensor.

 

[travs_dsm]

Thanks, I'll check the TPS as well. Hopefully it is something simple like that!

 

[pos4g63]

Have you checked the timing?

 

[travs_dsm]

Haven't checked timing yet. I figured since the car runs perfectly once it is underway it was something else?

Whatever it is, it is goofy and getting worse. At lunch today, I had to of course disconnect the Coolant Temperature Sensor to get it to start and then reconnect it before it tripped the CEL. Then when I was leaving the restaurant, it kept shutting off when I put it into reverse. It did this three times.

I went to Advance Auto, bought some Carb Cleaner and sprayed it along the intake manifold/head, vacuum hoses, intake etc... but it didn't change idle at all, so hopefully that rules out a vacuum leak.

In my warped way of thinking here is my theory:

When I disconnect the CTS, it causes the car to run rich and dump fuel which is allowing the car to start. Once started the idle sucks, but otherwise the engine runs fine: no missing, skips or anything else. I will test the coil and resistor, but I am really starting to think I have a fuel problem. Either an almost clogged fuel filter or a failing fuel pump.

 

[travs_dsm]

Well, the coil pack, power resistor and TPS all tested out good. I'm at my wits end trying to figure this out! I'm sure that disconnecting the CTS and having the car fire right up is a clue, but to what I'm not sure.

 

[Tyeler18]

Do you have a fuel pressure gauge? Stock fuel pump?

 

[zdravko_k2002]

I had a similar problem I was going crazy trying to figure out what it was tested out almost everything in the car, then I decided to check out my ECU sure enough it had leaking caps and a blown driver, so what i would suggest is you open up your ecu inspect it for anything that looks brown or burnt and send it to ECMLink thery can repair it for around $60, hopefully this helps!!!

 

[Tiki2777]

I would reset the ecu just in case and I would check your fuel injectors and throttle body. Hopefully you get this fixed soon, good luck.

 

[mitsukid02]

Haven't checked timing yet. I figured since the car runs perfectly once it is underway it was something else?

Whatever it is, it is goofy and getting worse. At lunch today, I had to of course disconnect the Coolant Temperature Sensor to get it to start and then reconnect it before it tripped the CEL. Then when I was leaving the restaurant, it kept shutting off when I put it into reverse. It did this three times.

I went to Advance Auto, bought some Carb Cleaner and sprayed it along the intake manifold/head, vacuum hoses, intake etc... but it didn't change idle at all, so hopefully that rules out a vacuum leak.

In my warped way of thinking here is my theory:

When I disconnect the CTS, it causes the car to run rich and dump fuel which is allowing the car to start. Once started the idle sucks, but otherwise the engine runs fine: no missing, skips or anything else. I will test the coil and resistor, but I am really starting to think I have a fuel problem. Either an almost clogged fuel filter or a failing fuel pump.

I would deff check the fuel pump and filter, i think you are correct on the CTS theory, when you un plug it, it doesnt know how cold/ hot it is, so it runs rich (protection for the motor) and that could also contribute to a crappy/ rough idle. Also if the fuel filter is clogged, or pump is going, that could explain the stalling and rough idle, i would look into that a bit more and confirm

 

[travs_dsm]

Read up some more on Coil Pack testing. I think I MAY have found a problem. So when I test where the plug wires plug in, I'm getting 12.72 and 12.79 kOhms of resistance which is within spec. However, when I tested the little three prong coil plug (primary?) I am out of spec. I am getting .01 Ohms(leads 1&3) and .02 Ohms (leads 2&3) on those leads. Does that mean the coilpacks are bad? There is a diagram halfway down through this thread that I am referencing:

back firing at wot, maybe fuel cut? - DSM Forums

 

[travs_dsm]

And of course, none of the local Mitsubishi dealers have the part in stock. Not sure I want to do the Autozone/Advance coil packs...

 

[BWeston]

And of course, none of the local Mitsubishi dealers have the part in stock. Not sure I want to do the Autozone/Advance coil packs...

Look on the classifieds for a coil pack and power transistor, they go for $40-$50, just to test out and identify the problem, it's worth it. You can always replace it with a new one later.

 

[travs_dsm]

Solid advice! I just ordered a used one from one of our supporting vendors to do exactly that! I hope this is it!

 

[travs_dsm]

Problem Resolved! It was a bad coil pack. I replaced it today and it fired right up, didn't have to give it gas or unplug the coolant temperature sensor! The idle is better too and it isn't shutting off in reverse either.

BTW, be careful when you remove your fuel rail that the little plastic standoffs don't fall off. Two of mine did and of course fell down through the holes in the intake manifold to the back of the motor. I had to go buy a flexible claw device to retrieve them! I was cursing like a sailor !

Thanks everyone for your help in my thread! I really appreciate it!

 

[Jazz]

I'm having the same issue with my car. I'm gonna try replacing the coil packs. Thanks in advance if it's my problem too. It'll save me alot of headaches and hair pulling.

 

[travs_dsm]

Spoke too soon. It wont start now, just endless cranking. Will test more later.