Okay, odd collection of symptoms now.

First, rough idle.
Then I get backfire through the intake, esp. right after start up if I give it throttle before it's fully warm.
Then it throws a p0305 code- cylinder 5 misfire.
Now I've got "wild vents" if I get on the throttle heavy. Vents are fine if rpm below 2,000. Go over 2400 and they go crazy.
Get 10mpg all city driving, but smells on the rich side.

Here's where we are at as far as recent maintenance:
* Brand new Champion copper plugs, less than 100 miles on them, properly gapped.
* plug wires properly routed per TSB, all wrapped in convolute.
* TPS, IAC, MAP, Crank, temp sensors all replaced within last 1,000 miles (Standard Motor t-series parts). Coil replaced at the same time.
* plenum fixed last winter with fel pro gasket and aluminum plate. Timing chain replaced with cloyes double roller set.
* fuel pump replaced with Delphi unit this summer
* Fuel injectors switched to four hole units, poor man's 50mm throttle body installed
* NGK O2 sensors installed last year with plenum repair

And the trouble shooting I did:
* no oil consumption, no coolant loss.
* getting good blue spark at plugs
* injectors are pulsing
* compression test this summer all between 145 and 160.


So, any ideas?

 

Wild vents; replace the check valves, and inspect for broken lines (where it goes through the firewall is a typical place of failure).

 

Do the compression test again.

 

What are you thinking there, HeyYou? Cracked head or blown gasket?

For the vents, I was wondering if it was an overall vacuum issue since I can recreate it easily under load as opposed to a failed check valve... Either a leak (that I don't hear) or maybe a failing cat backing pressure up?

Failing cat would cause a smattering of these other issues, right? Who knows how long the plenum was bad before I fixed it...

 

Failed check valve is common... the check valve isolates the low manifold vacuum state during acceleration/load from the rest of the system, and then relies on the vacuum reservoir to maintain the vacuum level in the rest of the system... failed check valve means the vacuum escapes, just as it does with a broken line... hence the comment about checking the line where it goes through the firewall, as this is likely the most common place that if fails... it chaffs through where it rubs on the firewall.

I would not rule out a sensor failure at 1000 miles, being SMP... since getting duds right out of the box, and low mileage failures, I buy factory from the stealership sensors now... the extra you pay for the sensors you save in your time doing the job over.

 

Bad valve seat, or similar problem.