420A hesitates under load

[SpeedEngineer91]

Alright guys, I'm stuck. '97 Eclipse RS; drives normal at about 1/2 throttle or less; any more than that and the engine falls on its face. It just sputters and shakes and doesn't rev any higher until you back off the throttle a bit. It's slightly better at higher RPM's, but still extremely present. It seems to run better when the engine is completely cold and it's also cold outside. Idle's basically normal, occasionally you can hear a slight miss. I'm getting 5 different codes:

p0108 - MAP sensor high input
p0113 - Intake air temp. sensor high input
p0123 - TPS high input
p0302 - Cylinder #2 misfire
p0340 - CPS circuit

...it's a mystery. So far I've tried:

New spark plugs
New plug wires
Checked coil resistances
New fuel filter
New air filter
Checked timing
New injectors
Checked compression (~150 across all 4)
EXTENSIVE searching for vac leaks, none found
Visual check of all sensor wiring, no rubs or breaks

I'm stumped; and I'm sick of spending money on guessing. Has anyone had a problem like this before? Any suggestions (fuel press. regulator? EGR? MAP sensor?)? Thanks for the help.

[david-b]

Well it says you have a MAP and CPS sensor problem. Any problems with the MAP or CPS will normally cause the car to run like shit. Buy a shop manual at AutoZone and it'll show you how to test all the sensor with a voltmeter to see if they're bad or not. Test the CPS, MAP, and TPS. The CPS will throw the misfire CELs because it doesn't know where the crank is and doesn't know how to fire in correlation to it's position. I'm sure once that is fixed, the others should go away.

[Adam-C]

Mine '99 GS has the same issue
If I floor it, no matter what it will hesitate, and the rpm's nearly refuse to raise. and the CEL starts flashing.
unless I back off to around half throttle.
(if i put the car in 3rd, around 20mph or so, and floor it, engine will backfire, sounds like from the intake, could be valve issue?)
I have my own OBD scanner, and it shows a P0302 engine code, nothing else.
I have done compression, fuel pressure, and vacuum tests, all came up clear. Car has had this problem for months, frustrating me to hell!

[SilvrEclipse]

Welcome to AF!

Try changing your plugs first. Make sure they are gapped correctly also.

[Adam-C]

New plugs, all gapped correctly, also checked the resistance of the plug wires and coil packs.
Thank you by the way.
I've done many tests in my high-school auto shop and even my autos teacher and a neighboring school's autos teacher were stumped.

[Cavalier9696]

Mine runs in reverse. When I gas on it hard it runs great, But at idle it wants to die. I have to gas on it for at least a minute before it idle's good.

[Adam-C]

within the next couple of days I will be venturing out to the local junkyard in search of a car with an in-shape 420a in it, then i'll probably just take the entire top-end off and see how much it will cost me.

[SilvrEclipse]

Adam, check your IAC and clean your throttle body.

[Adam-C]

Alright, but then why does my ecu record only a cylinder 2 misfire?

[david-b]

Originally Posted by Cavalier9696

Mine runs in reverse. When I gas on it hard it runs great, But at idle it wants to die. I have to gas on it for at least a minute before it idle's good.

Check for a leak somewhere around the throttle body. I blew my throttle body gasket over the weekend and had the same issue actually. Feel for an vacuum around there or spray some carb cleaner on the TB and see if it gets sucked in anywhere.