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Author Topic: Hesitation, Cold Idle, & Mileage Issues  (Read 2938 times)
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m3nate
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« on: August 15, 2016, 02:11:52 AM »

Hi everyone,

Having an issue with my '04 MSM.  Hoping for some help troubleshooting.  First, I have to admit that I am not totally familiar with the history of the car.  It was recently purchased and has 25,000 on the drivetrain.  The car does have the following Flyin' Miata parts installed:

1. Intake
2. Boost controller
3. O2 Modifier
4. Pop off valve

On to the issues.  Here's what I'm seeing.  I had another MSM previously, and am comparing the performance of this car to it.

1.  Idle issues when cold - The car will hunt for idle on start up for 2-5 minutes.  Goes between 300-1200 rpm.  Has died a couple of times when coming to a stop after first start up in the morning.
2. Hesitation - The car has a hesitation that manifests in 2 ways.  At 1/3-1/4 throttle slight "bucking" is present.  This goes away at 1/2 to 3/4 throttle.  At full throttle, the car has a huge dead spot in the RPM range.  When punched, it will GO, then no power, then at 5500 RPM it gets it's second wind.  The hesitation is abrupt enough to throw you against the seat belt. 
3.  Mileage - I'm getting 19 MPG consistently. 

I know these cars take off above 5000 rpm, at least that's what my last one did, and to expect progressive power delivery up to then, but the hesitation is fairly dramatic and not normal.  The mileage issue is troubling as I'm used to getting at least 24 MPG on my normal commute in the last car.

Thing's that I've checked:

1. Cleaned and lubricated "the bog" solenoid.  No change.
2. No CEL or codes
3. No obvious vacuum leaks. Have checked a couple of times and havent found one. 

I've searched for some similar problems and have found info on the bog and the hesitation, though nothing that seems to match my symptoms.

Thanks for reading!
- Nate

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SilverMiataRacer
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« Reply #1 on: August 15, 2016, 09:32:25 AM »

First you say you have a Pop Off Valve?  Do you mean a BOV, which all our cars have of some sort, or do you mean you have something like the Boost Fuse from FM that opens when a boost level is reached to stop over-boosting.

Second this car will not run well when it has not yet warmed up but the hunting is not normal and indicates a possible vacuum leak.  Sounds to me like you need to get the intake tract smoke tested.

Third the punch and then go issue is the normal ECU generated A/F-Boost delay.

The mileage issue is either your right foot or an indication of a problem and you need to start with the possible vacuum leak first and see what happens to the mileage.

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Larry

4 Miatas but who's counting!!   Cool

White Knight    1991 Crystal White   #99 CSP
Silver Bullet     1992 Silverstone     #17 SM2  FM I+ Turbo  (Gone but not forgotten)
Honey B          1992 Sunburst Yellow #99 SM2 J.R. M45
Whooosh         2004 Titanium MazdaSpeed MX5  #403 of 4000
Subie              2006 Steel Gray WRX STi Cobb Stage 2 (Gone but not forgotten)
No name yet    2008 Velocity Yellow Tintcoat Z06 Corvette
No Name yet    2014 Ashen Grey Metallic Camaro 2SS 1LE

“There are only three sports: mountain climbing, bull fighting, and motor racing. All the rest are merely games.”
– Ernest Hemingway
m3nate
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« Reply #2 on: August 16, 2016, 01:57:29 AM »

Thanks for the guidance.  It has an aftermarket BOv, different than others i've seen.  I was thinking vacuum leak as well due to the partial throttle bucking and hunting for idle, but for the life of me havent been able to locate one.  I'll take a run at the smoke testing and see what I can find.  I believe that the mileage is also related as I'm certain it's not a lead foot issue. 

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'95MSM
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« Reply #3 on: August 16, 2016, 05:00:22 AM »

BOVs have a piston that must be seated correctly in the "normal" (i.e. non-actuated, or not blowing off) mode. If the piston doesn't seat, there will be a significant vac leak.

If the BOV is a recirculating type (and it should be in order to not throw the MAF reading off), plug the hose that vents the BOV back into the intake plumbing pre-turbo and see if your idle stabilizes. I wouldn't drive it with the BOV disabled. If it is a vent to atmosphere style, you might try sealing it up with a balloon/finger cut off a rubber glove/condom/etc. If it is VTA, also do a search and read-up on how it dumps metered air, which throws off your a/f ratio momentarily.
« Last Edit: August 16, 2016, 05:06:14 AM by '95MSM » Logged

'05 running gear + '95 body
3.63 ring & pinion FM content: Blouch compressor mod, FM-Link, i/c & no-MAF intake.   BEGi: Stainless SGDP w/ metal core performance cat.   Custom stuff: Compressor clocked downward w/ new i/c pipe, big radius throttle elbow, 2.5" mid-pipe w/ Hushpower II, dual 2" axle-back w/ open Supertrapps, Toyota 4 pc cop ignition

245.2 whp on default FM-Link maps (with OEM midpipe)
m3nate
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« Reply #4 on: August 17, 2016, 01:42:58 AM »

BOVs have a piston that must be seated correctly in the "normal" (i.e. non-actuated, or not blowing off) mode. If the piston doesn't seat, there will be a significant vac leak.

If the BOV is a recirculating type (and it should be in order to not throw the MAF reading off), plug the hose that vents the BOV back into the intake plumbing pre-turbo and see if your idle stabilizes. I wouldn't drive it with the BOV disabled. If it is a vent to atmosphere style, you might try sealing it up with a balloon/finger cut off a rubber glove/condom/etc. If it is VTA, also do a search and read-up on how it dumps metered air, which throws off your a/f ratio momentarily.

Great additional guidance.  Question on this - When the car is started cold, it does not have the idle issue.  It only crops up once i've driven (can be 300 ft, .5 miles) and then when coming to a stop and sitting at a light, the idle issue occurs.  Is there another option to see if the piston is seated in the BOV aside from smoke testing if the idle is normal when I start the car and it's left sitting still?
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'95MSM
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« Reply #5 on: August 17, 2016, 06:06:11 AM »

Maybe you should look elsewhere - I don't see how driving the car would affect the BOV. If anything, I would think the vibrations of the car in motion would help the piston seat.

Does the idle issue go away if you put the clutch in? The neutral switch and clutch switch are, I believe, in the same circuit. A wonky idle that goes away when the clutch is depressed is often a neutral switch problem.

To the rest of our forum: does a failed or sticking neutral switch on the transmission throw a code?
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'05 running gear + '95 body
3.63 ring & pinion FM content: Blouch compressor mod, FM-Link, i/c & no-MAF intake.   BEGi: Stainless SGDP w/ metal core performance cat.   Custom stuff: Compressor clocked downward w/ new i/c pipe, big radius throttle elbow, 2.5" mid-pipe w/ Hushpower II, dual 2" axle-back w/ open Supertrapps, Toyota 4 pc cop ignition

245.2 whp on default FM-Link maps (with OEM midpipe)
Chrisbee
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« Reply #6 on: August 18, 2016, 02:22:07 AM »

If the idle problem goes away after the car starts to warm up, It could be the TPS. Which would also concur with poor gas mileage. Even though a CEL is supposed to come on with TPS issues. Try unplugging the TPS and running it like that to see if anything changes.
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2004 TI #3021. Purchased Oct. 2014 with 56k miles.

Engine: FM 2 kit with Hydra 2.7, 700cc injectors, and full 3" exhaust.
FM Crossflow radiator w/stage 2 airflow kit.
Suspension: Fox Racing with FM sway bars.
Wheels: 15x8 Enkei PF01s running 215/50 BFG G-force Sports.
Misc: Custom Speedhut boost gauge in place of stock oil pressure gauge. Temp gauge mod. ScanGaugeII. Blue instrument panel lights. Eclipse dash vents.

Definitely a work in progress!
m3nate
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« Reply #7 on: August 22, 2016, 02:11:15 AM »

Couple of notes from the weekend.

Vacuum leak - I performed a smoke test, which was successful in telling me that i don't have a vacuum leak.  Everything is tight as a drum with no leaks.  I used a blacklight to look around once the smoke had filled the system and there was nothing aside from the smoke escaping from the air filter.  I pulled the upper line from the brake booster and used that as my intake point, so im confident that the entire intake side was full. 

Idle & neutral switch - No change with clutch depressed/not depressed.

Next step - unplug TPS and see what happens.  That'll be this week.

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SilverMiataRacer
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« Reply #8 on: August 22, 2016, 09:30:54 AM »

The problem is your method for a smoke test is flawed.  Not saying you have a leak but you probably really failed to test the system.  Filling the system with smoke from the brake booster and leaving the filter open allowed the smoke to fill but not pressurize the system so if you had anything but a major leak it wasn't going to show.  The normal way to test the system would have been to fill it from the filter but filling it at the booster was okay but you needed to plug the filter opening so some pressure of a few psi would build in the system.
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Larry

4 Miatas but who's counting!!   Cool

White Knight    1991 Crystal White   #99 CSP
Silver Bullet     1992 Silverstone     #17 SM2  FM I+ Turbo  (Gone but not forgotten)
Honey B          1992 Sunburst Yellow #99 SM2 J.R. M45
Whooosh         2004 Titanium MazdaSpeed MX5  #403 of 4000
Subie              2006 Steel Gray WRX STi Cobb Stage 2 (Gone but not forgotten)
No name yet    2008 Velocity Yellow Tintcoat Z06 Corvette
No Name yet    2014 Ashen Grey Metallic Camaro 2SS 1LE

“There are only three sports: mountain climbing, bull fighting, and motor racing. All the rest are merely games.”
– Ernest Hemingway
m3nate
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Posts: 8


« Reply #9 on: August 24, 2016, 02:27:58 AM »

RE: the smoke test - Ah that makes sense.  I was continually filling the system, but without the adequate PSI, of course the trail is going to go path of least resistance.  I will take another run at it from the filter side and see if I can detect anything.  I did the old propane test as well on the intake side in all of the obvious areas, but didnt get any change in idle speed.  So that led me to believe that I may not have a leak...again, not a complete test.

Other update:  I did disconnect the TPS sensor and drove the car to and from work on Monday.  Results...interesting.

1.  The car would die almost every time i came to a stop.  Would not idle at all.
2.  When I refired the car after the multiple stalls, I got several backfires.
3.  Got a couple of backfires on deceleration when going from partial to 0 throttle.
4.  On throttle under acceleration and at high speeds the car ACTUALLY RAN BETTER.  The acceleration was much smoother and more progressive.  When letting off the throttle at 40-50 mph there was no bucking and deceleration was smooth as well. 

Im not sure what all of those items indicate.  Possibly that the TPS is shot?  It's new, but is not an OEM part....

Any thoughts?

Oh - and thank you all for the guidance to this point.  It is very much appreciated.
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SilverMiataRacer
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« Reply #10 on: August 24, 2016, 09:54:35 AM »

You don't have normal operation for running with an unplugged TPS so it can't be a bad TPS.
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Larry

4 Miatas but who's counting!!   Cool

White Knight    1991 Crystal White   #99 CSP
Silver Bullet     1992 Silverstone     #17 SM2  FM I+ Turbo  (Gone but not forgotten)
Honey B          1992 Sunburst Yellow #99 SM2 J.R. M45
Whooosh         2004 Titanium MazdaSpeed MX5  #403 of 4000
Subie              2006 Steel Gray WRX STi Cobb Stage 2 (Gone but not forgotten)
No name yet    2008 Velocity Yellow Tintcoat Z06 Corvette
No Name yet    2014 Ashen Grey Metallic Camaro 2SS 1LE

“There are only three sports: mountain climbing, bull fighting, and motor racing. All the rest are merely games.”
– Ernest Hemingway
'95MSM
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Posts: 6076


Turbo clocked downward, new i/c plumbing


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« Reply #11 on: August 24, 2016, 03:20:34 PM »

If it were me, and if I still lived 3 blocks from Mr. Hyde and could talk him into it, I would be installing his known-good TPS to see if the problems originate there. Throttle position is a fairly important input to the ECU.
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'05 running gear + '95 body
3.63 ring & pinion FM content: Blouch compressor mod, FM-Link, i/c & no-MAF intake.   BEGi: Stainless SGDP w/ metal core performance cat.   Custom stuff: Compressor clocked downward w/ new i/c pipe, big radius throttle elbow, 2.5" mid-pipe w/ Hushpower II, dual 2" axle-back w/ open Supertrapps, Toyota 4 pc cop ignition

245.2 whp on default FM-Link maps (with OEM midpipe)
SilverMiataRacer
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« Reply #12 on: August 24, 2016, 04:43:47 PM »

Yea, but if it was his TPS then unplugging it should make it drive like all the cars without the TPS drive and that's not what is happening to him.
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Larry

4 Miatas but who's counting!!   Cool

White Knight    1991 Crystal White   #99 CSP
Silver Bullet     1992 Silverstone     #17 SM2  FM I+ Turbo  (Gone but not forgotten)
Honey B          1992 Sunburst Yellow #99 SM2 J.R. M45
Whooosh         2004 Titanium MazdaSpeed MX5  #403 of 4000
Subie              2006 Steel Gray WRX STi Cobb Stage 2 (Gone but not forgotten)
No name yet    2008 Velocity Yellow Tintcoat Z06 Corvette
No Name yet    2014 Ashen Grey Metallic Camaro 2SS 1LE

“There are only three sports: mountain climbing, bull fighting, and motor racing. All the rest are merely games.”
– Ernest Hemingway
mr_hyde
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« Reply #13 on: August 24, 2016, 09:16:00 PM »

I have a spare TPS and Throttle body but it is always easier to do part shuffles in the driveway rather than through the mail.
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2005 Black Mica #290 8/27/04 w/Factory Hard Top
BEGi Intake, FM Downpipe.  Nice and calm with an edge...

1990 Red - MSM Drivetrain, Adaptronic EMS, Xida 700/400, 15x9 6uls, Full Cage, SGDP w/80mm Corksport exhaust, ~260whp @ 15psi on Forged Rods.  bow2
Build Thread: http://www.mazda-speed.com/forum2/index.php/topic,24668.0.html

2000 BMW M5 - The Falcon - Daily Driver  reddevil

2003 E350 7.3 Powerstroke Ambulance for towing '90MSM to play dates.

1991 BRG - Daughter's daily driver.
m3nate
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« Reply #14 on: August 25, 2016, 01:42:34 AM »

Makes sense RE: TPS.   Everything symptom-wise points to a vacuum leak I believe.  I just havent found it yet.  I havent looked deeply into possible injector sealing issues, and I am thinking that may be a next step to pursue.
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