I have a 97 Protege 1.5L 5-Speed with 250 km. I have a couple of small issues and I am struggling to find a solution.

1. When I come to a stop and the engine is warm (never happens when it's cold), the engine slows to idle and begins to vibrate like it's about to stall (shifter is in neutral). However, if I release the brake pedal (with the car still stopped at a light and the engine idling), the engine does not vibrate/struggle anymore and idles normally. What could be causing this?

2. When I start moving again from a stop (again, this only happens when the engine is warm), the whole car starts to shake, as if I released the clutch too quickly and didn't give enough gas. If I release the clutch quickly, on the other hand, and with the same amount of gas, it shakes maybe once or twice. It feels almost as though the engine is not producing enough power (I have 10 yrs experience driving stick, and have never had this happen). It only happens when the engine is warm and only from full stop. Why is this happening and is it related to the previous problem?

3. This has been happening for a couple of months and the CEL came on a couple weeks ago. Came up EGR fault code, so I opened it and cleaned it. The code hasn't come back, but now fault code P0420: Catalyst System Efficiency Below Threshold (Bank 1) came up. So I changed the front O2 sensor which was showing the wrong resistance, and after resetting the CEL, it didn't come back on.... until the other day. I was driving on the highway and came to my off ramp. While down-shifting from 5th to 4th, RPMs went up and CEL came on - P0420 again. Why?????

I have am pretty good with doing repairs myself, and I do own a OBD2 scanner. I tried to be as detailed as possible because my problems occur only under those conditions, otherwise the car runs well. Does anybody know if these problems are related and/or how I can diagnose and repair?

Thanks

 

I think I would at least check the brake booster for a vacuum leak. It sounds like the brakes being depressed has something to do with it. Just a thought.

 

Thanks! I'm definitely going to check the vacuum system for leaks this weekend. Do you think that a leak in the vacuum system could be causing the P0420 fault code?

 

Can someone give me an idea of which hoses to inspect? I haven't found a vacuum leak so far but I may be missing a hose

 

New update: I have come to realize that the RPMs drop at idle when the engine is warm when the brake AND clutch pedals are pressed. I don't know why the clutch is involved, does anyone have any ideas?

If it helps, these are the readings I'm getting from my OBDII reader:

Engine Warm, Gear in Neutral, Handbrake pulled, Clutch and Brake pedal NOT pressed:

FUELSYS1 OL-DRIVE
LOAD_PCT(%) 15.3
ETC(degF) 205
SHRTFT1(%) -25.0
LONGFT1(%) -4.7
RPM 1045
VSS(MPH) 0
SPARKADV(deg) 10
IAT(degF) 52
MAF(lb/min) 0.320
TP(%) 9.8
O2B1S1(V) 0.885
SHRTFTB1S1(%) -25.0
O2B1S2(V) 0.915


Engine Warm, Gear in Neutral, Handbrake pulled, Clutch and Brake pedal PRESSED:

FUELSYS1 CL
LOAD_PCT(%) 18.4
ETC(degF) 210
SHRTFT1(%) 0.8
LONGFT1(%) -5.5
RPM 820
VSS(MPH) 0
SPARKADV(deg) 1
IAT(degF) 64
MAF(lb/min) 0.288
TP(%) 9.8
O2B1S1(V) FLUCTUATES FROM 0.820 TO 0.065 (NOT IN SYNC WITH 02B1S2)
SHRTFTB1S1(%) FLUCTUATES
O2B1S2(V) FLUCTUATES FROM 0.800 TO O.285 (NOT IN SYNC WITH 02B1S1)

 

I had a similar problem with rough idle when stopped waiting in traffic. I was not able to determine I had a spark plug problem (just one) until I looked at the engine at night time. It was immediately clear that a spark was not getting all the way down to the plug cause it was arcing across the top of the valve cover from the plug wire to the valve cover.

I would take a quick look at night just to make sure that is not the problem.

I replaced the spark pug and the 4-6 inch plug wire connector and now it is fine.

Thanks
Mark
2000 Mazda Protege 1.6 DOHC

 

I too have had this issue with my Mazda 6.
It was a bad brake booster, internal leak. It actually caused a lean code. And 2-3 times it was lacking brake pressure!
After this they finally found it.

 

interesting... your numbers look about right. stft is ok and engine load too. maf numbers too. so i would eliminate the vacuum leak (my first thinking when reading your post). clutch should not be a thing to consider here unless it is dragging on the flywheel, and thus, trying to stall the engine. when you press the clutch, you are dropping 200 rpm....but again... gear in neutral? have you notice any strange noises? strange unless your release bearing is all messed up.remember that the release bearing contacts the clutch pressure plate and that is bolted to the flywheel. do this. get those numbers again: 1) car warm, neutral, handbrake engaged, press brake pedal only. then repeat with no brake and just the clutch. and again with no brake and no clutch. just a start. will need more info to help better. its just the clutch thing that bothers me.....

 

just realized that this is a 2 year old post!

 

At least my response was to a new one!

Recycling at it's best.