Intermittent Idle Fluxuation, Runs Rough, Loss of Power

KEVINO67

MEMBER
2000 MAZDA PROTEGE
186,000 MILES

I have no CODES. Check Engine Light is OFF. Car is a 2000 Protégé, 1.6L Auto, 186,000.100% factory setup Issue is intermittent Runs worst when cold. Engine starts fine, throttles up to ~2500 RPM, then falls on its face and drops to 100 RPM, some times stalls out, some times stays running. After a few minutes the fluxuations decrease to a 900-500 rpm range. It is not steady, nor predictable. Car will appear to run fine, stop at a light and it will almost stall, then when the gas is depressed, has a loss of power. All these symptoms happen at varies times, sometimes its only one thing, some times several, sometimes all issues, some times it runs fine and purrs like a kitten. Based on advise from the blogs the following have been replaced.
New Plugs, New Wires, cleaned the injectors (these looked fine) replaced the MAF, Replaced the IAC, removed and cleaned the EGR (had black exhaust on it), cleaned all the EGR ports and lines, replaced the Vacuum lines. Cleaned the Throttle body. When the car is idling fine, I Have sprayed every where with starting fluid to check for vacuum leaks, it seams OK there. The snorkel between the throttle body and Air box appears to be in good repair. (The Air filter box does have a broken ear on the non-latching side, but I have installed screws to hold that side tight.) After the car runs rough, I go home, open the hood to diagnose and it runs fine. It does seam more pronounced when cold. Also, I can sometimes hear a quiet popping noise from the exhaust at idle. Covered the exhaust output with hand and can feel exhaust. (It burns the throttle body cleaner out with white smoke after cleaning, so I don't think the cats are blocked) Mileage is still in the 28-30 range in the city. Once underway under normal driving conditions, there are no noticeable issues. IT did give a P0421 Warm Up Catalyst Efficiency Below Threshold (Bank 1) once this summer, I cleared the code and it has not returned. The 2 front O2 Sensors where replaced 12 months ago, due to check engine faults.

3 Replies

TY ANDERSON

MECHANIC
684 POSTS

One thing you mentioned about the exhaust that flagged me is the exhaust noise. Is it a ticking noise that is load at a cold start-up? Or noise goes away when engine is warmed up? If you have an exhaust leak up stream from the any of the pre-catalyst O2 sensor can cause intermittent drive ability issues. The reason for this is the exhaust can cause outside air to get sucked into the exhaust (where the exhaust leak is) diluting the oxygen content in the exhaust effecting the O2 sensor input signal to the computer. This causes the vehicle's computer to enrich the air/fuel mixture to maintain 14.7 to 1 ratio.

You've covered some of the most common issues with the parts that have been already replaced.

Lastly, check the battery terminals clamps for corrosion and grounds. Make sure the electrical connections are tight and clean.

Let me know what you find.

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Thursday, November 21st, 2013 AT 5:02 PM

KEVINO67

MEMBER
2 POSTS

Thanks for the reply. No its not always at start up or cold. It is not a tick. It is a very quiet release of air sound. It is very intermittent. Some days no issues. It all most sounds more like it is hitting on 3 or the 4 cylinders. I just ordered new coil packs @ 33$ ea on line, so that is my next attempt. It never does nt get up and go, some times it falls flat when I leave a traffic light, stumbles for a sec, then goes. But it is like 1 in ever 15 lights. I wis the ECU would throw a code. But I have no codes, no light, no stored codes. I have un hook bat and reset computer (like and hour), new bat, all connections look clean.

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Friday, November 22nd, 2013 AT 7:23 AM

TY ANDERSON

MECHANIC
684 POSTS

Another couple of parts that could cause intermittent issues are the purge valve sticking open causing a rich condition resulting in a rough idle. Or the E.G.R. Valve could also be sticking open causing a inert gases to dilute the air/fuel mixture.

Do you have access to a scan tool that can show the live data stream for the engine.

You'll need to capture when this stumbling issue occurs. Short term fuel trim (STFT) percentage should be under +10% and above -10% at idle. Anything past that there is a vacuum leak or restricted fuel injector (or leaking injector depending on the STFT percentage).
If you could get any data at idle send it to me and maybe I might be able to seem anything out of the ordinary.
If not it might be best to leave this one to a reputable diagnostic shop because it could be more than parts. For example, a worn through wire might ground itself out only when you accelerate disrupting the data supplied to the vehicle's computer. Which you'd think would trigger a service engine soon light. The check engine light or service engine soon warning (which ever your has) doesn't light up every time it detects an issue. The computer will do self tests and if the testing passes or doesn't cross the threshold enough times to trip a check engine light.
Good luck!

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Friday, November 22nd, 2013 AT 5:15 PM