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fine on startup, 3rd startup it started missing, not idling.


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Hello everyone,

 

I have been searching on here for an answer with no luck or similar symptoms so I figured Terry would know, here is the story. The 99 CSVT  went in to get trans removed. Once I got it back we put everything back together minus exhaust 3 weeks ago, just had headers on (was waiting for more parts) Started the car to make sure it would run after the trans replacement. It started fine and idled nice, motor sounded good. I did this twice within a few hours and it was fine. Later that day I started it and it would not idle, had to keep my foot on the gas. Yesterday I connected the full exhaust and its worse, still not idling and missing horribly. When I hold the gas down to around 3k, the motor will die and rev back. When it does idle it does so roughly at 500 rpm.

 

What has been done:

1: The egr downpipe had to be replaced due to a stripped nut on the header side. (could dirt have clogged something in the intake from not cleaning the pipe?)

2: Checked all connections & large wiring harness with bolts in them also.

3: performed a tune-up (coil, wire, plug) OEM

4: replaced new tune-up parts with old tune-up parts to eliminate chance of multiple issues

5: Checked plugs and all are firing, no wet plugs and they were all warm after a few sec of attempted run time

6: Checked all vac lines

7: cleaned iac, egr

 

 

My diagnosis with a guess would either be dirt clogging the intake or something electrical. Does anyone have another suggestion?

Thank you in advance for your input

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I forgot to mention the car will start but instantly quit, unless i press the gas. The fuel filter has been replaced since this problem started. I went and checked the up stream O2 sensors and they were connected well. I have MIL's on the 2 downstream sensors, didn't think those would make the car not run. Yes the fuel/ mix issue is possible, not enough fuel perhaps. It likes backfiring. Its strange how it was fine, hours before it went belly up. I will have to get a pressure gauge to check the fuel pressure i suspect.

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following your fuel/ mix theory i went and unplugged the MAF sensor. The car actually idles when i went to start it. When I plug the sensor back in while idling there is a click and the car runs like shiz and dies...guess thats the problem.

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No difference with the new MAF, no codes, wet plugs and unburned gas exiting the exhaust. I have checked and rechecked every connection with no luck. I dont understand why it runs horribly. Im stumped, guess ill take it to the shop. Will report back.

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..wet plugs is a bad spark situation.I'd re check the plug/harness to the crank position sensor, they tend to  go bad ,also check the 3 large plugs on the front bracket of the cam covers above the alt belt etc, they also may not be making a full connection if they are not fully 'clicked' home...

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I would bet on a severe vacuum leak. If you have a major leak the MAF will cause the engine to run poorly, and disconnecting it will allow the engine to run off of strategy instead of real time data. Aside from having any spark plug wiring issues (backfiring) the actual backfiring comes from fuel that is not being pulled into the cylinders completely and is sitting in the manifold. Poor manifold vacuum can be caused from a leaking EGR gasket, intake gaskets, vacuum lines disconnected, throttle body gasket or PCV system (disconnected).

 

I would check these, easy check is to connect a vaccum gauge - Normal is 15-21 inHg at idle. Anything below 15 indicates a leak.

 

-Dom

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  • 4 weeks later...

Thanks Terry and Dom  for your responses, I swapped out every sensor I could from my other 99 parts car, all with no difference made, put the originals back on of course,Terry you were correct at the air fuel mix. The UIM and LIM gaskets were leaking.  Car is now fixed and runs like a she devil! So the car sat for 6 months, I would have never thought that the gaskets would go bad, would a back fire situation or a clogged exhaust cause the gasket to fail? The car ran great before the trans broke.

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