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Shakes bad at 1000 RPM gas pedal on floor

Tiny
DRMALOY
  • MEMBER
  • 1998 MAZDA 626
  • 112,500 MILES
Car will only start if I hold gas pedal to the floor and runs only for a short bit. It shakes bad and is maybe at 1000 rpm gas pedal to the floor

Engine had a tune up and told IAC valve needs replaced. Car began making noise in engine by belt side. Was driven 1 mile following day and it died while driving. Unable to restart. Installed a new IAC valve and checked plugs they were wet. Checked for spark and had good spark. Fuel pumped humms for couple seconds when key goes to start.

fuel pressure seems good. Engine ran okay then all this the next day. Any help would be greatly appreciated.
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Tuesday, September 18th, 2012 AT 6:49 AM

21 Replies

Tiny
KHLOW2008
  • MECHANIC
  • 41,815 POSTS
Have the battery and alternator charging checked. The belt noise could be a fault with the harmonic damper and this can result in improper charging.
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Tuesday, September 18th, 2012 AT 7:46 AM
Tiny
DRMALOY
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  • 11 POSTS
Engine turns over fine its not the charging system. When it fires up it shakes the engine and now barely reaches 500-600 rpm
going to do a fuel pressure test today and see if there is a leak.
Will the fuel pressure regulator hold vacuum. Or if it leaks is there a problem with it.
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Tuesday, September 18th, 2012 AT 4:47 PM
Tiny
KHLOW2008
  • MECHANIC
  • 41,815 POSTS
It shuld hold vacuum. Idling speed is to low. Have the throttle body and IAC cleaned.
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Tuesday, September 18th, 2012 AT 5:57 PM
Tiny
DRMALOY
  • MEMBER
  • 11 POSTS
Did A Fuel pressure test and it seems good.
Cleaned the throttle body with some spray. I got the car to stay idle but it has a slight surge. Any attempt to give it gas it surges more and shakes but will only get to 1000rpm and then want to die. It idles with the air mass sensor removed. At idle I put it back on and it died. Any ideas, thanks
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Tuesday, September 18th, 2012 AT 7:26 PM
Tiny
KHLOW2008
  • MECHANIC
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Did you check for trouble codes?
Is the Malfunction Indicator Light indicating?
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Tuesday, September 18th, 2012 AT 8:09 PM
Tiny
DRMALOY
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  • 11 POSTS
Engine light has not come back on. Had a p1506, & changed idle air control and cleared it.
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Tuesday, September 18th, 2012 AT 8:24 PM
Tiny
KHLOW2008
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Was it a new or used IAC that was replaced?
Are you still having difficulty starting?
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Wednesday, September 19th, 2012 AT 1:09 PM
Tiny
DRMALOY
  • MEMBER
  • 11 POSTS
It was a new IAC. It starts but has erratic idle and you have to hold gas pedal sometimes to get it to start. Unable to rev engine at all. Any ideas.
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Wednesday, September 19th, 2012 AT 7:33 PM
Tiny
KHLOW2008
  • MECHANIC
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No trouble codes with symptom description. I can only think of the following that can cause that.

1. Throttle Position Sensor.
2. Mass Air Flow Sensor.
3. Valve clearances.
4. Engine Coolant Temperature Sensor.
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Wednesday, September 19th, 2012 AT 8:11 PM
Tiny
DRMALOY
  • MEMBER
  • 11 POSTS
My fuel pressure test was 60_70 specs are 35_45psi
I am going to redo pressure test to make sure and check vacuum to fuel regulator
Should the fuel regulator hold vacuum with key off.
Will also check throttle position sensor and position.
Changed engine coolant temp sensor and when starting cooling fans came on
Immediately. Is that normal?
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Thursday, September 20th, 2012 AT 2:51 AM
Tiny
KHLOW2008
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At 60 psi the pressure is too high and can mean a bad fuel pressure regulator or clogged return hose/pipe.

Fuel pressure regulator vacuum should drop when engine is not running.

Cooling fans are not working correctly. The ECT could be wrong or you have a problem there.
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Thursday, September 20th, 2012 AT 5:51 AM
Tiny
DRMALOY
  • MEMBER
  • 11 POSTS
Re did fuel pressure test and it sat around 40
twice I turned the key hearded the fuel pump run and the pressure was real low. Then again it sat at 40 while engine struggled to keep at idle. I applied vacuum to fuel regulator and it dropped by maybe 5psi. I checked MAF sensor, IAT sensor, coolant temp sensor, camshaft sensor, TPS and calibrated it to the book
NO codes are showing up. Engine is running just as bad no matter what. Any ideas.
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Thursday, September 20th, 2012 AT 8:11 PM
Tiny
KHLOW2008
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Have the engine compression tested.
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Thursday, September 20th, 2012 AT 8:23 PM
Tiny
DRMALOY
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  • 11 POSTS
Did compression test and readings are around 200psi high
Book says standard 171 & min 119
Too much carbon build up?
Would all this engine running erratic cause plugs to be black, carbon?
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Friday, September 21st, 2012 AT 8:36 PM
Tiny
KHLOW2008
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Yes, erratic or rich running would cause sooty conditions. So would bad spark plugs. They can short out after running rich.
200 psi seems pretty high and carbon build-up cold be one reason.

Try a new set of plugs to see if it helps.
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Friday, September 21st, 2012 AT 8:44 PM
Tiny
DRMALOY
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  • 11 POSTS
What causes the inability to rev up the this engine
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Saturday, September 22nd, 2012 AT 5:01 AM
Tiny
KHLOW2008
  • MECHANIC
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We don't know yet. Possible causes are :

1. TPS.
2. MAF.
3. Fuel pressure.
4. PCM

If you have a scan tool, plug it in to monitor the various sensors and if there are trouble codes get them.
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Saturday, September 22nd, 2012 AT 8:44 AM
Tiny
DRMALOY
  • MEMBER
  • 11 POSTS
No codes yet, put new plugs in no difference, checked compression again all reading around 150, on first stroke and end around 200 210.
Is there a way to test pcm. Thanks
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Saturday, September 22nd, 2012 AT 5:00 PM
Tiny
KHLOW2008
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Nope, You can only use a known good PCM to substitute to test.
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Saturday, September 22nd, 2012 AT 5:20 PM
Tiny
DRMALOY
  • MEMBER
  • 11 POSTS
Broken tensioner spring for the timing belt caused it not to run.
Car runs now and has thrown p301 and p1506.
I checked cylinder 1 spark plug and adjusted gap and p301 went away. I have no engine light coming on but if I scan it I get P1506. I replaced IAC and received same code again. Car is idleing at 1050 rpm. I am thinking idle is set wrong. No vacuum leak noticed. Any other ideas before I adjust idle?
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Tuesday, October 2nd, 2012 AT 7:04 AM

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