Fluctuating RPM at idle - Page 2

Dec 2, 2015 | 12:33 AM

#26

ironj221

Thread Starter

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Joined: Feb 2008

Posts: 44

Likes: 1

My issue was indeed the fuel injectors. Sea Foam solved it, so I'd recommend that as cheap option #1.

May 13, 2023 | 10:03 AM

#27

Tomo

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Joined: Apr 2023

Posts: 2

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I have a similar problem:
The engine is several thousand km after rebuild and recently something like this happened:
The idle speed of the engine began to rise and fall with regularity exactly every second (it didn't seem random) by about 500 revs.
Even when I added gas and kept it at about 4000 rpm. it still happened with the same accuracy.
After less than minute it just stopped (not the engine

) and since then (+-300km) nothing like that happens.

Any ideas?
Should i be worried?

May 13, 2023 | 10:23 PM

#28

Left4Dead

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Joined: Nov 2021

Posts: 146

Likes: 12

I would look for vacuum leaks
Clean and reset the ess sensor
maybe even bad gas
if not then there are more things after to check but those are first

May 14, 2023 | 04:26 PM

#29

gwilliams6

40th anniversary Edition

Joined: May 2008

Posts: 2,951

Likes: 142

From: Grapevine, Texas

Quote:

Originally Posted by Tomo

) and since then (+-300km) nothing like that happens.

Any ideas?
Should i be worried?

RX8 Engine Power Loss

chokes as revs increase
- O2 sensor failure (too rich)
- MAF failure
- MAF disconnected
- e-shaft sensor fouled
- accessory belt fraying
high end power loss (hard fuel cut)
- Rev limit reached
high end power loss (jerky and stumbling)
- Ignition failure
- fuel pressure loss
- e-shaft sensor fouled
high end power loss (smooth)
- Catalytic converter clog
- air filter clog
low end power loss (smooth)
- Engine compression loss
low end power loss (stumbles)
- Ignition failure
- front O2 sensor failure
revs slowly but smoothly
- O2 sensor failure (too lean)
- catalytic converter clog
- air filter clog
sudden power drop at a specific rpm
- Intake valving actuation problem
trouble getting to redline
- Ignition failure
- front O2 sensor failure
- catalytic converter clog
- air filter clog
- e-shaft sensor fouled
- fuel pressure loss
- MAF failure

May 24, 2023 | 08:03 AM

#30

sethstephens21

New Member

Joined: May 2023

Posts: 9

Likes: 0

Quote:

Originally Posted by ironj221

My issue was indeed the fuel injectors. Sea Foam solved it, so I'd recommend that as cheap option #1.

so I have the same issue as you it fluctuates from 750 maybe even lower sometimes back up to 100 to 1200. Would you recommend seafoam to help me with this issue? I have a gutted cat and sounds like an exhaust leak but I have exhaust leaks on my other cars and they never do this. Sorry for years late response but I just found this thread.

May 26, 2023 | 02:24 PM

#31

icemantbi

Registered

Joined: Jun 2009

Posts: 147

Likes: 7

From: Sault Ste. Marie, Ontario

Check coils. wires and plugs. When I had a rough idle like that, it was time to change out the coils, wires and plugs. That fixed it for me.

May 28, 2023 | 08:16 PM

#32

cfletcher592

New Member

Joined: Feb 2023

Posts: 2

Likes: 0

From: New Jersey

Quote:

Originally Posted by gwilliams6

Generating Power at Full Throttle
• Ignition Coils
• Spark Plugs
• Spark Plug Wires
• Engine Compression
• E-Shaft Sensor (ESS)
• Air Filter
• Intake Valving
• Throttle Body
• Mass Air Flow Sensor (MAF)
• Fuel Pump
• Fuel Injectors
• Catalytic Converter (Cat)

Keeping the Engine at a Cruise
• Ignition Coils
• Spark Plugs
• Spark Plug Wires
• Engine Compression
• E-Shaft Sensor (ESS)
• Intake Valving
• Throttle Body
• Mass Air Flow Sensor (MAF)
• Fuel Pump
• Fuel Injectors
• Front O2 sensor
• Catalytic Converter (Cat)

Keeping the Engine at an Idle
• Ignition Coils
• Spark Plugs
• Spark Plug Wires
• Engine Compression
• E-Shaft Sensor (ESS)
• Mass Air Flow Sensor (MAF)
• Front O2 sensor
• Catalytic Converter (Cat)
• Intake Vaccum

im having this issue and I hope I’m lucky I think it’s my cat since it is smelling like gas 24/7 my exhaust has a really bad rattle to it and it also take awhile to pick up speed.

May 28, 2023 | 10:32 PM

#33

Loki

Registered

iTrader: (1)

Joined: Jun 2009

Posts: 8,389

Likes: 1,107

From: Montreal

Quote:

Originally Posted by cfletcher592

im having this issue and I hope I’m lucky I think it’s my cat since it is smelling like gas 24/7 my exhaust has a really bad rattle to it and it also take awhile to pick up speed.

Yeah you're going to want to stop driving it and check the cat, and replace if necessary before it takes out your engine.

Nov 26, 2023 | 06:52 PM

#34

sethstephens21

New Member

Joined: May 2023

Posts: 9

Likes: 0

Quote:

Originally Posted by icemantbi

Check coils. wires and plugs. When I had a rough idle like that, it was time to change out the coils, wires and plugs. That fixed it for me.

I’ve had the coils wires a plugs changed for awhile, I’m still having idling issues, fluctuating from as low as 500 up too 1500 back and forth. I checked my solenoids for good connection my connectors are fine but idk if the solenoids are good. Anyway to check that without a voltmeter? Also air pump delete was done on this car as well. Comp is good seals are good engine was rebuilt. Just having these idle issues. Wonder if it’s a pcm problem. Guy before me says he went too have it tuned but doesn’t think the guy put a “real” tune on it. Somebody please help me

Nov 27, 2023 | 02:51 AM

#35

gwilliams6

40th anniversary Edition

Joined: May 2008

Posts: 2,951

Likes: 142

From: Grapevine, Texas

Quote:

Originally Posted by sethstephens21

RX8 Engine Power Loss

chokes as revs increase
- O2 sensor failure (too rich)
- MAF failure
- MAF disconnected
- e-shaft sensor fouled
- accessory belt fraying
high end power loss (hard fuel cut)
- Rev limit reached
high end power loss (jerky and stumbling)
- Ignition failure
- fuel pressure loss
- e-shaft sensor fouled
high end power loss (smooth)
- Catalytic converter clog
- air filter clog
low end power loss (smooth)
- Engine compression loss
low end power loss (stumbles)
- Ignition failure
- front O2 sensor failure
revs slowly but smoothly
- O2 sensor failure (too lean)
- catalytic converter clog
- air filter clog
sudden power drop at a specific rpm
- Intake valving actuation problem
trouble getting to redline
- Ignition failure
- front O2 sensor failure
- catalytic converter clog
- air filter clog
- e-shaft sensor fouled
- fuel pressure loss
- MAF failure

Starting the Engine

Starter
Battery
Engine Compression
Grounding Wires
Ignition Coils
Spark Plugs
Spark Plug Wires
Fuel Pump
Fuel Injectors

Generating Power at Full Throttle

Ignition Coils
Spark Plugs
Spark Plug Wires
Engine Compression
E-Shaft Sensor (ESS)
Air Filter
Intake Valving
Throttle Body
Mass Air Flow Sensor (MAF)
Fuel Pump
Fuel Injectors
Catalytic Converter (Cat)

Keeping the Engine at a Cruise

Ignition Coils
Spark Plugs
Spark Plug Wires
Engine Compression
E-Shaft Sensor (ESS)
Intake Valving
Throttle Body
Mass Air Flow Sensor (MAF)
Fuel Pump
Fuel Injectors
Front O2 sensor
Catalytic Converter (Cat)

Keeping the Engine at an Idle

Ignition Coils
Spark Plugs
Spark Plug Wires
Engine Compression
E-Shaft Sensor (ESS)
Mass Air Flow Sensor (MAF)
Front O2 sensor
Catalytic Converter (Cat)

Last edited by gwilliams6; Nov 27, 2023 at 02:55 AM.

Jun 25, 2024 | 12:35 PM

#36

cmaderia10

Registered

Joined: Oct 2010

Posts: 246

Likes: 10

From: Wilmington, Massachusetts

Have you tried resetting the ECU. That’s what I did when my car was stalling out. Search for resetting the ECU; rx8club.com. do both ECU reset procedures (odometer reset button and brake pedal). Then, start the car. And without revving it, let it run for 20 minutes at idle. It will reprogram your idle. Hope it helps

Chad

Last edited by cmaderia10; Jun 25, 2024 at 02:56 PM.

Jan 20, 2026 | 08:28 PM

#37

G305an

Registered

Joined: Nov 2025

Posts: 2

Likes: 0

Same issue 2004 rx8 manual

Quote:

Originally Posted by Dolpho69

Clutch neutral safety switch. When you press the clutch in, does it go away?

I changed everything changeable. I did all tests possible, and everything fine. Check neutral switch and cables are melted and wires touching. Rpms only fluctuate when clutch is released.