Source
r/Miata•
Teeque87

Hesitation on low rpm - cold start only

Hey Guys,

I'm trying to track down an issue with my 91' NA that I really want to pin down before I spend maybe hundrets of dollars to fix it.

Those issues occur only on occasion and only on cold start and seem to get worse or happen more often on colder weather especially below freezing.

The car starts just fine any day, any temperature but is hesitating to accelerate on cold start every now and then (not all the time). Also only happens like twice or three times in total until everything sorts out pretty much.

It also seems to be only happen on high load and or low rpm (around 2k ish). Almost like the car needs to think if it should accelerate or not for like maybe 2-3 seconds and then suddenly really pulls.

I've recently changed the timing belt, ecu temp sensor, sparkplugs (ngk bkr6e-11 had bkr5e-XX before), spark plug wires, oil and the airfilter.

The reason why I changed the sparkplug wires was corrosion in on of the plugs on the coils (cylinder 4). I cleaned up all the corrosion as good as I could when I had it off for the timing belt job. The ohms also seem fine and are right within spec.

Have you guys an idea what could be wrong and or what is causing it? I'm not that experienced yet on cars in general but my guess would be coils are bad or maybe the injectors.

Regards

Posted Apr 24, 2018, 9:40 AM UTC · edited

317
MakoDaShark'01 Crystal Blue•

Huh, I have a very similar behavior in my 01. I start up the slight hill of my road and at like 2.5 to 3k it will suddenly start pulling hard. I try to shift early if I have a passenger to not cause whiplash.

3
Teeque87OP•

Does the rpm also seem to be stuck for a few seconds before it actually revs up like it normally would?

1
MakoDaShark'01 Crystal Blue•

Maybe a little bit, I always figure it's a combination of cold start, uphill, and me not being aggressive. But once it hits 3k it's like I've stepped on the pedal more.

2
neruphuyt'01 SE•

I've noticed the same thing in my '01. I figured it was the vvt though.

1
MakoDaShark'01 Crystal Blue•

Yeah, that would make some sense with cold oil, good call.

1
QwucEx 91 Mariner, current 01 matte black.•

It is your VVT. If your car isn't warmed up and you pass 3000ish rpm you'll feel a kick from it engaging. It's a good indicator imo when your rpms are to high and your car isn't warmed up. I try and keep it below 2500 before warming up.

1
undeadQueequeg1992 NA6•

If it's just a little hesitation in cold weather and the engine is running smoothly (not breaking up) when it's happening, I wouldn't worry too much. My daily driver (not a Miata, old gasoline Benz) does this as well and I can even tell when the ECu shifts from warmup-mode into normal mode because the car will suddenly start to accelerate lightly on its own instead of maintaining speed, forcing me to lift off the accelerator a bit.

I haven't noticed anything like this with the Miata, but I typically don't drive that when it's cold outside.

2
HailRawks•

I just replaced the coils on my 1990 NA and it is now like a new vehicle. Had no low end grunt and felt like my clutch was going bad. I always thought coils were either good or bad and not much in between, Picked one up for $60 on amazon prime. Also, there is a bolt on the back side of it that is a tough one so you will need a 12mm ratcheting wrench. The new coil does not use this third bold. So you can just put it back with the spacer and washer and the new coil bracket fits right over it.

2
Teeque87OP•

You had those issues only on low rpms aswell? Apart from that my car feels perfectly fine though. Pulls hard, doesn't stall, smooth idle. Mine only had 2 screws in when I removed it to inspect it and replace my ecu temp sensor.

I doubt that we have that coils on our german amazon but I've seen one for around 100€/ ~120usd. Maybe I should just give it a shot.

1
HailRawks•

Yes, mostly from a stop and at low RPM's. I didn't have enough torque for the clutch, but it felt like a slippy clutch was the problem. Then I would kind of have to gun it to go from a stop. I think mine was sort of ok when still cold, but warmed up was worse. I can feel a big difference in all over performance now. The reason I changed the coil was because my son's Jeep XJ started missing on a cylinder because the coil was bad on #3. I replaced the coil pack and the jeep jumped to life. I couldn't believe the difference. Same for my 28 year old NA coil. I guess wasn't giving a big fat spark any more.

1
Teeque87OP•

Hey mate quick response, I replaced my coilpack just today.

Feels a lot better now, had some small hesitation on first launch but it did disappear almost instantly after.

Cylinder 4 Port on the coilpack had blueish corrosion on it. Cant be good I guess.

1
CommonMisspellingBot•

Hey, Teeque87, just a quick heads-up:
alot is actually spelled a lot. You can remember it by it is one lot, 'a lot'.
Have a nice day!

^^^^The ^^^^parent ^^^^commenter ^^^^can ^^^^reply ^^^^with ^^^^'delete' ^^^^to ^^^^delete ^^^^this ^^^^comment.

0
Colonel_of_Wisdom•

Check the timing on your CAS also. When in cold start mode your ecu retards timing and runs slightly richer.

2
Teeque87OP•

I did check it twice and set it to bone stock 10°. Thanks for your input though

1
Colonel_of_Wisdom•

Gotcha. I had the same issue and I changed mine from 8deg to 12 and it is much better now.

1
Teeque87OP•

Even though my post is 1 month old. I bumped mine to about 14° now and it really feels much smoother, especially on cold starts.

2