MEGAsquirt A place to collectively sort out this megasquirt gizmo
Sponsored by:
Sponsored by:

Bad Idle, But Only Sometimes

 
Old 05-17-2019, 01:28 PM
  #1  
Junior Member
Thread Starter
iTrader: (3)
 
Join Date: Jan 2014
Posts: 145
Total Cats: -3
Default Bad Idle, But Only Sometimes

Hey everyone, I need a hand on getting this weird idle issue figured out. I had my car tuned by a company, but the idle / CL idle seemed a little underwhelming.

I'm very much so still learning but I've changed several settings and have about a halfway consistent 900 rpm idle. The issue is when the car enters closed loop at 1200 rpm, the engine rpm will start to get jerky. It will drop down to around the 900 rpm target but still it will almost seem like the engine 'coughs' and the rpm will rapidly drop. Oscillation isn't the right word, and i'm not sure if misfire is the right one either. Anyways, it's random. I could be coming to a stoplight and it could enter idle great - no pops or jerky engine at all. I could then creep forward or just rev the car a little, and it would do it's thing where it coughs and has a rougher idle. I've tried to turn closed loop idle off, and still experience this. I had been using adaptive idle advance before but it made this much worse so I've turned it off until it's figured out. When it's got the weird idle, when I give it gas to take off from a stop it stumbles momentarily when I give it gas. When it's idling great, I can take off smooth as butter.

The setup:
Poverty DIYPNP with GM AIT sensor, batch fire. The car is a stock engine 96' with a Flyin' Miata based turbo kit. Flow force 640cc injectors. Newer spark plugs. The engine has good compression and leakdown numbers.

The log:
Idling poorly, throttle blip, then the idle settles in perfectly.

Worthy mentions: the car idled beautifully on the stock ECU and when I switched to the DIYPNP it did this weird idle thing on the stock injectors and the flow forces also. The cars alternator squeals a little bit on startup.

Thanks!
Attached Files
File Type: msl
BadIdleLog.msl (266.4 KB, 8 views)
File Type: msq
BadIdle.msq (115.9 KB, 6 views)

Last edited by festersays; 05-17-2019 at 02:23 PM.
festersays is offline  
Old 05-17-2019, 01:52 PM
  #2  
Junior Member
 
Join Date: Nov 2016
Location: Columbia, MO
Posts: 137
Total Cats: 10
Default

"The cars alternator squeals a little bit on startup."

-Get a new belt, tightening it probably won't do much by now. You can try and see if it fixes it.

Sounds like the PID is off a bit and is causing the closed loop to overshoot. I'm not able to look that the tune or log at the moment. Just a guess.
thebigtuna is offline  
Old 05-17-2019, 02:20 PM
  #3  
Junior Member
Thread Starter
iTrader: (3)
 
Join Date: Jan 2014
Posts: 145
Total Cats: -3
Default

I'm 99.9% sure it's the bearing inside the alt rather then the belt. I did a timing belt service maybe a year and a half back, replaced the belt with a brand new Gates and it's doing the same. For fun I went and had the alt. tested and it came back good from an electrical standpoint. I am not going to discount anything so I'd be happy to try a new belt.

I don't disagree that it could be the PID, but since it's happening with closed loop disabled wouldn't that sort of rule out the CL settings?
festersays is offline  
Old 05-17-2019, 02:27 PM
  #4  
Junior Member
 
Join Date: Nov 2016
Location: Columbia, MO
Posts: 137
Total Cats: 10
Default

"I don't disagree that it could be the PID, but since it's happening with closed loop disabled wouldn't that sort of rule out the CL settings?"

-Yeah idk then since I can't look at anything. I get the idle overshoot occasionally but i haven't felt like fixing it because it's not often for me. I need to do it one of these days.

As far as thinking its the bearing, I would be surprised if it is. Take the belt off and spin it by hand, that will tell you if its the bearing or the belt. How do you know the timing belt is doing it as well? Are there squeals from two different areas on start up? Do you have A/C and PS?
thebigtuna is offline  
Old 05-17-2019, 02:40 PM
  #5  
Junior Member
Thread Starter
iTrader: (3)
 
Join Date: Jan 2014
Posts: 145
Total Cats: -3
Default

I'm bad at explaining stuff. I replaced the alt. belt while doing the timing belt service. When I had the alt off to get it tested, I spun the bearing by hand and could hear where it would squeal. I really should just replace both at some point. But yes, I do have both AC and PS.

With any luck we'll both find a solution. Thanks!
festersays is offline  
Old 05-17-2019, 03:18 PM
  #6  
Supporting Vendor
iTrader: (9)
 
nigelt's Avatar
 
Join Date: Aug 2014
Location: Carmel Valley, CA
Posts: 1,208
Total Cats: 196
Default

It is just me, or does it take a second after you blip the throttle for the revs to jump up? In the logs there's a a half second delay between you pressing the throttle and the RPM even starting to move, and a full second between your throttle depression and the revs jumping to 1800. If that's true you'd definitely feel it.
__________________
FlowForce 380 |640| 960 Injectors
LS Coil PNP harnesses
and complete kits
Free shipping on everything,
including MS3Pro PNP
Bring your own boost - goflowforce.com
nigelt is offline  
Old 05-17-2019, 03:54 PM
  #7  
Junior Member
 
Join Date: Nov 2016
Location: Columbia, MO
Posts: 137
Total Cats: 10
Default

ASE or VE too rich and choking it out?
thebigtuna is offline  
Old 05-18-2019, 09:11 AM
  #8  
Junior Member
 
Join Date: Nov 2016
Location: Columbia, MO
Posts: 137
Total Cats: 10
Default

Hmm,

You could bump up the 90RPM 10 MAP cell of the ignition table to make it smoother. Could also add a column to the left of your target idle column and bump it up a degree over what you are targeting to help with idle droop. It will simulate what the idle advance does for load, as far as i understand. I don't see anything crazy with the tune or log unfortunately. It looks like its hunting in the beginning part of the log, which is what is bothering you correct?


"It is just me, or does it take a second after you blip the throttle for the revs to jump up? In the logs there's a a half second delay between you pressing the throttle and the RPM even starting to move, and a full second between your throttle depression and the revs jumping to 1800. If that's true you'd definitely feel it."

-Definitely looks like it has a decent idle dip before and isn't triggering AE till the last second when it triggers MAP AE.

Does the car free rev well if in neutral and giving it a little blip? Or does it hesitate OP?
thebigtuna is offline  
Old Yesterday, 12:21 PM
  #9  
Junior Member
Thread Starter
iTrader: (3)
 
Join Date: Jan 2014
Posts: 145
Total Cats: -3
Default

Sorry for the delay, I wanted to put some miles on the car to help answer the questions better. The idle dip that you guys mention when I get on throttle is absolutely noticeable when it's hunting and I rev it. It dips significantly, and the engine sounds like it's breaking up/missing until the rpms rise above abou 1000. If it's idling normally (which it does most of the time) I don't notice really any hesitation or delay. Maybe a SLIGHT delay? But certainly no dip or anything of that nature - it revs smoothly like it should. I will try your suggestions Tuna and report back. I agree that what you're saying about adding a row maybe at 750 with higher timing could help.

Thanks again!!
festersays is offline  
Old Yesterday, 01:15 PM
  #10  
Junior Member
 
Join Date: Nov 2016
Location: Columbia, MO
Posts: 137
Total Cats: 10
Default

No problem buddy! Hope it works out for you.

"when it's hunting and I rev it. It dips significantly, and the engine sounds like it's breaking up/missing until the rpms rise above abou 1000."

- Not surprising at all. It's struggling and then a bunch of air is shoved into the motor. Something is making it the mixture lean imo. Once again all guesses. Hope smoothing out that idle area of your ignition table helps out.

That's really strange and hurts my brain though. Symptoms sound similar to my car on a hot restart before I got the issue resolved. Seems like its running lean but the logged AFR looks fine. Is your wideband showing the same as tunerstudio?
thebigtuna is offline  
 
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
turbogrill
Supercharger Discussion
45
Yesterday 11:57 AM
jtt
General Miata Chat
18
05-15-2019 07:53 PM
2yan
Build Threads
5
05-15-2019 02:17 PM
Keuzy
Engine Performance
9
05-15-2019 12:54 PM
xmacmiatax
MEGAsquirt
7
05-15-2019 07:43 AM


Thread Tools
Search this Thread
Quick Reply: Bad Idle, But Only Sometimes


Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.