Car Bucking/Stumbling/Hesitating/Misfiring

Some Background on the car/possibly relevant information:

- Car is a '92 Laser RS Turbo FWD 5-Speed
- Car is 100% bone stock
- ECU is original, non-EPROM ECU (i.e, no Link to log with)
- Always garage stored and never winter driven until this last year, so all rubber is soft and pliable, all wires are still very malleable/flexible
- All new belts/fluids
- New NGK BP6RES plugs
- New OEM NGK Wires
- New O2 Sensor
- New (ECU) Coolant Temp Sensor (Gauge and A/C Temp Sensors still original)
- NO Check Engine Light (it does work, has been verified)

The Issue:

On cold starts or when the car has sat for more than a few minutes the car will misfire like crazy, buck and surge. Even just sitting with the car in neutral if I give it more than a light (few %) pedal input or try to rev it up it just starts misfiring like nuts. If I drive it it will buck and surge if you give it anything more than a few % pedal. Additionally, the car will either not hold idle or will have a weak/varying idle.

When the car has been driven for a while (15+ minutes usually) it starts to slowly get better and less noticeable but it takes at least 30+ minutes of driving before the issue mostly goes away. At this point it still does have some surging under certain conditions but mostly drives 'normally' besides the wonky (but better than before) idle. Also at this point, WOT tip-ins are pretty much normal.

Now, I assume it is something electrical/some sensor because even if the car is hot (e.g. being driven for a few hours continuously) and then I turn it off for 10 minutes and start it up again the issues reappear, just not as exaggerated as after the car has sat for a few hours/overnight. That is to say, I believe you could fill the car with oil and coolant at 210F first thing in the morning and the problem would still be just as terrible as if the car were cold and alternatively, if you drove the car for 2 hours and dropped in freezing cold coolant/oil the problem would be barely noticeable just as it was with the hot fluids. I should note that ambient temp does seem to play a bit of a role - cold mornings always exaggerate the problem much more than starts on a hot, 35 degree afternoon when the car's been sitting outside in the sun all day.

As mentioned, the car has all the maintenance done with lots of new little bits (as it had sat for a few years prior to me buying it last year) and I've done a thorough inspection of the engine bay on a few occasions in an effort to try and tackle this problem. I've also tried spraying water and carb cleaner at any possible air leak location but did not find anything (have not done a BLT thus far as it is quite a hassle on a car that is 100% stock with every little bracket and hose still in place). Additionally, I have replaced the PTU with a known working one. I do have a spare coil pack that I can swap in but none of the recent changes (O2 sensors, Coolant Temp Sensor, PTU) have seemed to make any difference so I'd like to see if anyone has any ideas before I go down too many other paths.

I have not removed/inspected the ECU yet but that may be my next step.

Any insight in this matter would be much appreciated as it's getting worse and it's to the point the car isn't really driveable unless it's been running/driven for quite some time (which you can't easily do...)!

Have you tried new transistor?
Do you have a palm pilot or scan master? I have a scan master for sale!

I had a fuel leak that dripped on my transistor and the car started running on only two cylinders, your sounds like it's not as bad but figured I would throw it out there.

PTU = Power Transistor Unit, so yes I've tried a 'new' (i.e. known working) one.

I have a palm pilot buried away somewhere (good luck finding it) but it was never used for logging - I had it long before I even had a license. I don't have a scan master either. Don't really have the funds to purchase anything more than the most absolute necessary items right now.

Oops, haha my bad.
I think you need a logger on there because if it's a sensor you will know right away.
Tried another ECU?

You didn't read what I wrote did you...hahaha:



A logger would be nice but I'm not taking the ECU out of the talon and redoing all the settings just to get link in the Laser temporarily and I'm not buying a logger setup/Link for a car I have every intention of keeping 100% bone stock, at least not right now as the funds are very limited. If someone has a setup I could borrow that would be great, otherwise I'll have to do it by troubleshooting/inspection/multimeters (for certain sensors)/etc.

Going old school here

My bad struggling, right before I posted that I went back to see what you had tried then suggested it, haha.

Do you have an old laptop? I think with a serial cable you can connect up to your setup. A full logger setup should be less than 100 with the palm and cable, pretty sure my palm was 30$

tada!!! http://www.ebay.com/itm/Palm-M105-new-in-box-/262038152643?hash=item3d02b0e5c3

Here we go better option that way you can just use your laptop
http://www.ebay.ca/itm/Mitsubishi-U...1-PLUG-/181782627508?hash=item2a5316c4b4

Let's put it this way...unless it is 99% absolutely necessary I am not spending money. I just don't have it to spend (right now). $30 US is nearly a tank of gas and when you spend $100+ on gas in an average week that makes a difference. If someone has one to lend me temporarily that's great but at the current time it's not in the cards to acquire anymore equipment.

Also, no old laptop that has a serial connection, unfortunately.

Got you, fair enough.

I would be testing that coil pack you have and inspecting the ecu before I try finding someone with a logger.

Almost sounds like the ECU as Bryan mentioned. Swap in the ECU from your other DSM or another known good ECU. That should help you narrow it down.

Sounds sort of coil related..Try anything with that?

I say coil pack or ECU. Try swapping coil packs as that's super easy and go from there.

I was about to say: the cost of that O2 sensor would have gotten you most of the way to a logging setup, which I'm confident you could use to immediately find your problem..

..then I remembered you still haven't paid me for it

I'd also say coil packs or ECU, leaning more towards ECU though since coil packs tend to act up when they get too hot.

As I mentioned, ECU is the next step. Just wanted to confirm that idea. Have located a working spare one to go in (not taking the one out of the Talon - too much work although the logging capability would be nice) and also have a few spare coil packs.

Was just trying to do things one step at a time (PTU only, then only coil pack, then O2 Sensor, then Coolant temp sensor, then only ECU) vs. doing things in a batch because that doesn't really tell you what what specifically is the issue.

I'll report back with findings.

I would swap in a known good MAFS for a moment after the boost leak test.

Locating a good, known working 1G MAF is getting to be a harder task these days as most get tossed or have been modified in some way.

If the both the coil pack and ECU changes make no difference then that would be the next item on the list. After that....well...hopefully it doesn't get that far!

No kidding! Hopefully it doesn't get there. You could try unplugging the MAFS and see what happens to the idle. If it smoothes right out, it could mean the other parts are OK. But, it could also point back to the ECU.

I may have a MAF sensor from that 1g. I'll look and let you know.

Sweet! Let me know what you find Would be nice to grab as a spare even if I do get the car running well again this weekend.

I'd also check your emissions system for vacuum leaks and possibly a stuck EGR valve, sounds like the car is running lean on initial start up, I have a handheld vaccuum pump you can borrow if you need one.

Boost Leak Test is on the list of 'to-do's' but as mentioned I did do a thorough spraying with both water and carb cleaner and neither had any effect on the engine speed (drop or increase).

How would I check for a stuck EGR valve? I've never had/worked on a DSM that actually still had one on it (or if it did I blocked it off).

I'll be back in Toronto this weekend - will try and be in touch with you if time allows.

I'm not convinced it's the ECU at all... If it's the ECU, it would most likely persist no matter how long the car was run for.

Do you have any way of checking your fuel pressure?
I'm thinking it would be a PTU, Coil, or something fuel related. I had those exact same symptoms when my fuel pump was on it's way out, albeit not at startup...

If you're in Toronto this weekend and still want a 1g MAF, let me know. I've got a spare here you can have.

Unbolt the EGR and use a vacuum pump on the ports to see if the diaphragm holds pressure and if the plunger doesn't get stuck while it's in motion. There's a few different styles but there's diagrams available online to show you which port is which.

I don't have a way to check fuel pressure but I'm not convinced that it's the fuel pump because of the behaviour of the car and the fact that the issue gets reduced some/completely at WOT depending on how long the car has been driven already.

PTU it's definitely not, coil I intend to change this weekend. ECU I will also change this weekend if it's not the coil. MAF and EGR may or may not get tested/changed this weekend depending on timing and outcome of coilpack/ECU.

I'll shoot you a message about this and borrowing the pump. Thanks again.



Thanks. Will try and stop by to grab that from you at some point this weekend.

The fact that it gets better over time suggests that it may have something to do with temperature...? Just brainstorming over here.

Coil pack first I'll put $5 on it. lol

Agreed that it may have something to do with temperature, but not the temperature of the engine (coolant/oil)...temperature of the item causing the problem though, yes, to an extent. Or some other property which changes over an extended period of time.

I actually tried to change CP a few weeks ago because it was one of my main suspects but it was putting up a fight to come out and I just haven't had a chance to get back at it. Hopefully I'll have a little more time this weekend to get it out. Looks like I may have to crack the fuel rail loose to move it out of the way a bit as even with all the bolts undone (even the hidden one) it doesn't quite want to come all the way out.

If you've got a spare coil pack handy I believe there's enough room to just unplug the old one and connect the new one without having to unbolt anything.

I do have one handy - it's in my trunk right now. I'll see if I can fit it in there. As I mentioned, car is 100% factory stock so there's a lot of extra brackets and pieces in the way that I never even knew existed.