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90 Mazda MPV: van..the 3.0/automatic with 180,000 miles..rough idle

Resolved Question:

I have a 90 Mazda MPV van with the 3.0/automatic with 180,000 miles. It has been running real good but it has developed a rough idle recently. There is slight pressure in the valve covers. When I take the oil filler cap loose, it makes it idle real rough. If I pull the dip stick it does the same. I replaced the PCV valve but that didn't help. Any suggestions?

Submitted: 7 years ago.
Category: Car
Expert:  Car expert replied 7 years ago.

this rough idle does it smooth out if you spray a little starting fluid in it?

the egr valves somtimes stick open on these

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Customer: replied 7 years ago.
No. Of course it speeds up momentarily, but then no change in the rough idle. When I remove the oil filler cap it all but dies. at a high idle it runs great.
Expert:  Car expert replied 7 years ago.

if you just give it a little start fluid does it smooth out?

it may be a vacum leak or and ignition trouble


Customer: replied 7 years ago.
As it revs up from the starter fluid it runs smooth, but then when it idles down again it is rough. Sometimes it will idle smooth but when I open the oil filler cap it really gets rough.
Expert:  Car expert replied 7 years ago.