Changed spark plugs - now car hesitates/dies off idle ?!?

I just changed the spark plugs and air filter (OEM) in my 2005 2.5i wagon, it was running just fine before, but now it stumbles, hesitates and dies off-idle.

 

I gapped the new NGK BKR5EGP plugs to .76mm before installing, and torqued them down to 14 n-M (reduced the 21 n-M torque by 1/3 because I used anti-seize on the threads, per the manual). The car has 120K on it, I have changed them every 30K miles since I bought the car with 60K miles on it.

 

I removed the plastic pipe that goes from the air filter box to the engine to access the plugs, and I forgot to re-connect the electrical connector after I got done. When I fired it up, the check engine light came on and cruise control light blinked. I figured out what I did, re-connected it, and that fixed that. I don't think that has anything to do with my current problem, but thought I'd mention it.

 

I double checked, and I am 100% sure each spark plug wires is connected to the correct cylinder, and that they are fully connected to the plugs. (I felt both the initial faint click, then second more definite click when pressing them onto the plugs.)

 

I'm stumped, any ideas?

I've always been told to NOT gap Subaru plugs. This might be since they are iridium but I just put the plugs in right out of the box and all was well...but I do have 1 step colder plugs on a GT so it is a very different case...

 

GL with the solution!

Yeah i never gap NGK plugs and i never use that type of NGK plug you should use FR5Ap-11 plugs. If it ran fine before the issue is def something askew with the plug installation if you have the old one put them back in and see it if fires and runs fine. If so then go get another set of the correct plugs and install them NOT per the gapping instructions in this manual you referenced.

 

 

I wrote a HOW-TO for this process you should read it

Did you by chance switch a spark plug wire (i.e. put 1 in 2 or 3 in 4 or vice versa)? Otherwise I would say disconnect the battery for ~30 minutes to an hour (just to be safe), hook it back up and see if that fixes the issue.

Yeah i never gap NGK plugs and i never use that type of NGK plug you should use FR5Ap-11 plugs. If it ran fine before the issue is def something askew with the plug installation if you have the old one put them back in and see it if fires and runs fine. If so then go get another set of the correct plugs and install them NOT per the gapping instructions in this manual you referenced.

 

 

I wrote a HOW-TO for this process you should read it

 

I was going to use FR5AP-11 plugs, but they were only available by special order at Autozone. Their parts computer cross-referenced an Autolite plug or the NGK BKR5EGP plug, so I went with the NGK's because I wanted to git-er-done this weekend.

 

I checked the gap on the BKR5EGP plugs before installing them, and they were about 1mm. BTW the manual I was using is the factory service manual. page IG(H4DOTC)-5 says the gap should be between 0.7 and 0.8mm.

I just went to O'Reilly Auto parts, and FR5AP-11's are special order only there too. I guess I'll have to bend over and get some from the stealership tomorrow.

 

Odd that a NA, non-performance type engine would be so finicky about spark plugs!

Did you disconnect the battery to do anything? If so, how long did you let the car run for after reconnecting it? This happend to me a few months ago, after reconnecting the battery I only let the car run for 2-3 minutes and it would stall on me when I would engage the clutch. Disconnected battery for a little bit again, but let it idle for 10 minutes after and all is good.

Did you disconnect the battery to do anything? If so, how long did you let the car run for after reconnecting it? This happend to me a few months ago, after reconnecting the battery I only let the car run for 2-3 minutes and it would stall on me when I would engage the clutch. Disconnected battery for a little bit again, but let it idle for 10 minutes after and all is good.

 

Actually I didn't tell the whole story about the electrical connector I forgot to put back on. The first time I fired it up after changing the spark plugs (when I forgot to reconnect the wire to the airbox) , I got the check engine light/flashing cruise light. I realized the problem, re-connected the wire, and started it again, I got the check engine light/flashing cruise light. I disconnected the battery for about a minute, thinking maybe I need to reset the code. I started it up again, and no check engine/flashing cruise light. After that, I only drove the car around the block, definitely less than 10 mins.

 

Is that common for the car to run rough for some period of time after the battery is disconnected? Does the ECU need time to re-calibrate itself maybe?

Yes after you reset the ECU it has to learn things again and it will run rough until it is back up to speed. You left the MAF sensor unplugged but after you plugged it back up you should have reset the ECU again and unplugging the battery won't do that, you have to unplug the battery and dissipate all store electricity in the system. This is simple just honk the horn turn on lights press brake pedal, then reconnect the battery. It should take the engine a few times turning over to crank but this is normal.

 

 

Yeah the computer x-refs those plugs but I am not sure why they are for a EJ255 not a EJ253 i believe they say they are a different iteration of the required plug. Are there anymore symptoms ? Once you put the right plugs in we know that part is back to normal, have you verified wires are correct?

After driving around a bit, the hesitation problem went away on its own. I guess the ECU just had to get back into the swing of things after the battery was disconnected.

 

However, just so I can sleep better at night, I replaced the BKR5EGP's with FR5AP-11's (I left the gap as they came at 1.1mm). Seems to be running a wee bit smoother now.

 

Thanks all for the replies!

GEE-OTTO is right treat your car like you would yo mama, with respect. hehe Glad to see you used the 11's. LOL

I'm still having the same issue...

After a spark plug change the car now idles funny then dies. So I did the ECU reset a few times, tested the MAF to see if it's working(it is), then cleaned the MAF out. But I still getting a engine code p0171(running lean.)

 

STI 07 68k miles

 

NGK Iridium IX Spark Plug LFR7AIX

what vacuum hose is off? u take the brake booster off?

what vacuum hose is off? u take the brake booster off?

 

Only things I took off when changing plugs was battery and the intake box. I don't think I took any hoses off but I'll double check everything.

2005 Legacy GT 88,000

 

I just removed my intake manifold to get to the water pipe seal that was bad (Cam x 2, Crank, Coolant S., throttle coolant, vacuum lines, ignition coil connectors, fuel lines, and battery). When I reinstalled my intake I tried running car and it idles rough and stalls. When up the RPM it makes it better but it still has a lot of shake then comes back down to stall. How do I know I put the coils connectors back onto the correct plug. I am not getting an error code, it comes up as pass. It ran fine before I did this till I saw I had a coolant leak.

 

Any suggestions? Thinks to look for? Everything seems hooked up as suppose to be. I have a ground that I dont know quite where it goes, looks to be one that would go on the intake manifold. Could this cause it?

 

Just put in a new rebuilt engine and turbo, getting frustrated to get it back on the road!