99 Escort spark knocking badly after replacing air filter

Hello, I have a question on my 99 escort. Today I replaced the air filter, the car was running fine and the engine was quite as a sewing machine up untill this point. After I replaced it drove up town and the
car was spark knocking so badly I was concerned it would damage the engine and it started immediately after changing the air filter. When I got back home took the new filter out and put the old dirty one back in and the engine was instanley smooth and quite again. Also with the new filter it was idling much higher and very hard to crank. I hate running it with the old filter but would rather do that than listen to the engine sounding like it was coming apart. What would cause this? Also I replaced the old filter with the same exact filter, a fram from wally world. Anyone else ever experienced this?
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It sounds like replacing the air filter lowered the vacuum just enough that the EGR valve does not actuate. Check all the vacuum hoses for cracks or disconnection.
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On Sat, 14 Aug 2010 01:34:28 -0400, snipped-for-privacy@webtv.net wrote:

I do not know for sure if the Excort uses a mass air sensor but, if it does, you may need to clean it with some residue free electronic cleaner. Ping is a common occurence if it is contaminated with debris such as excess oil from a K&N filter or if the engine has excess crankcase vapors. The usual fix for that is to make sure the PVC system is working correctly.
Lugnut
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wrote:

Would sound good EXCEPT - the OP replaced Fram with Fram, and when they put the old one back in, it ran well again - making the MAF a longshot and the reference to K&N totally irellevent.
The EGR is the most likely scenario af those mentioned so far.
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