D15Z1 VTEC-E engine in a '95 Civic VX HB.

Everything is fine first thing in the morning (and even when the engine's sat all day and gotten 'cold') - runs great. Once the temps come up, the engine 'surges' when the throttle is in the 'sweet spot' between accelerating and decelerating while cruising. I also notice the problem when the 'upshift' light comes on between gears. I've also noticed the throttle seems largely unresponsive if I get pissed and attempt to go WOT when this 'issue' occurs - seems like something is preventing the throttle from moving while the surging is happening, but is fine any other time. This also happens whether or not the A/C is running, so I can't blame the IAC (which is new, too).

New filters (fuel, air, oil), new synthetic oil, new OEM NGK plugs, new coolant and OEM radiator, new head gasket, and about 850 miles since the last tune-up (with all the new stuff). I even pulled the plastic insert away from the backside of the grill opening, which is providing even more cooling to the engine. The last thing I've done to the engine is replace the Intake Air Temp sensor, which also turned off the CEL. Once that happened, the I reset the ECU and it seems happy now - to the point that the 'upshift' light now functions (it didn't before in CEL 'limp mode').

My theory is that the ECU is the cause of this issue - probably because it's getting bad information. When it was in limp mode, I didn't have these issues, although it was annoying with CEL being on.

I'm not willing to write off the ECU just yet, because I've got another 150 miles before resetting the valve lash and timing (since I had the head redone after the previous owner blew the head gasket and warped the head). I had set the timing to 17 BTDC @ 750 rpm while I had the paperclip jumper plugged into the 2-port diagnostic plug under the glove box. The engine runs smooth and had decent power (for what it is) in limp mode.

Since it seems temperature related, I'm going to try a few things with the IAT sensor - 1st, pull it out and replace the old one into the intake, hoping that the ambient temperature of the engine compartment 'fools' the ECU. If it seems to help, I'll try wrapping the sensor with some electrical tape, hoping to dull the sensitivity to help it even more. If that helps as well, then I'll reinstall the new IAT sensor back into the intake and see what happens. I don't want to just unplug it altogether, because that'll just kick the CEL again - even though it will run better (IMHO).

Anybody else experienced this before? If so, hook a brutha up and let me know how you fixed it - unless it involved an engine swap... that's not an option at this point in time, since this is my econo-box experiment. If the little VTEC-E blows up at some point, I'll try and find a B16 or something to replace it. But for now, I gotta make it work.

 

Nobody?

I pulled the new IAT sensor, zipped-tied it up and out of the way, and put the old one back in the hole. It didn't really seem to help much - but then again, I wasn't very optimistic that it would do much. I only drove it a few miles (made a run to Subway for dinner), and didn't really hammer it either.

I'm going to try some more troubleshooting later this week and see what happens. Worse case scenario, I wind up unplugging it altogether and running in limp mode with the CEL on and putting a piece of limo-tint over it.

 

what were you trying to do with the IAT sensor outside of the intake manifold? just see if the hot air in the engine compartment made it run different?

you could also try and run the IAT to the outside where there is cold air, that might make a difference, but i know the sensor itself isn't really a huge deal if its not connected and the CEL is on. and if it runs better that way who knows. did you pull the CEL code to see what it was?

 

Yes - the CEL code was indeed the Intake Air Temp sensor (flash code '10'), and the new sensor turned off the CEL without even resetting the ECU - which I did anyway.

And yeah - I was hoping to see if the underhood air temp would be any better than the intake air temp, keeping in mind that the intake manifold itself is actually hot to the touch at operating temps. My laser thermometer indicates that where I zip-tied it to was much cooler than the intake manifold itself - 109 degrees against the firewall vs. 146 where it normally lives in the intake.

But, I'm guessing that my little experiment is moot and the IAT sensor has nothing to do with my issues.

Hey - it was something to try and the price was right - guess I know not to waste any money on a CAI now. I'll put it back to 'normal' tomorrow after work and get serious about figuring it out. I was hoping someone had experienced (and fixed) this before, though.

 

Nice Jeep, BTW [ef4life]. Here's a link to a pic of mine: http://www.mister4x4.net/off%20road/EricJeep2.jpg

 

Anybody have any input? Anything?