Erratic Idle/Acceleration/Deceleration - Need Help

[HotRaud90]

After experiencing a stutter while accelerating at low and high rpms, I changed the spark plugs and COPs yesterday. After putting everything back together, I cranked her up and took her for a test drive. Started fine, let her warm up a bit, then drove at some normal speeds for a bit, tested the RPM range. Then I went WOT. Everything felt super smooth again. No hesitation, no stuttering. Yay.

After about 20 minutes of driving, I started noticing some odd play in the way the car accelerated and decelerated. Sometimes I'd go to ease on the gas from a stop and the RPMs flat line, slightly dip, then spike up and the car would jolt into acceleration. This was not due to a downshift. It was like it was taking a second to think about the throttle input. When letting off the pedal, I would experience a harder than normal decel. Deceleration is normally smooth, this was a little more abrupt.

Then today, when I started the car cold in the morning, it started and RPMs climbed near 2k as normal, then as they came down it dipped all the way down to where the car was almost stalling out, around 100-200 rpms. I let the car die. Started again, same thing, then it would slightly sputter back up to around 600-800 then go back down to 100 while all but stalling. I revved the motor a couple times, only to have it dip way below a 1000 rpms once I let off. Finally after holding throttle at about 1500 for 5-10 seconds, it started to normalize slowly.

Driving normally, I experienced the same thing as yesterday. Delayed input of the throttle from a stop, more abrupt decel once I let off the pedal, mostly while in 1st-3rd gear.

WOT feels great, very smooth, no hiccups at all. I really only experience the delayed throttle intermittently when I'm accelerating from a stop or when I'm beginning to accelerate after braking and slowing down.

I'm at a loss. The only out of the ordinary things that happened were that I drove for a bit without one of my coil cover bolts on. Lost it while replacing plugs and COPs. Had to drive about 30 minutes without it until I could get a replacement. Even then, the coil cover was on, just not bolted all the way down.

Also, I fiddled with my throttle body a bit while I had intake tube off. Pulled throttle a bit so I could see inside upper intake to inspect for build up. I cleaned off the face of the blades with a rag and pulled throttle back and forth to test the play in it.

I'm at a loss. Wanted to give a detailed description as I couldn't find anything of this nature when searching the forums. Saw similar stuff, but nothing exactly like this.

Before anyone says anything about it, it hasn't been that long since I cleaned the IAC, MAF, cleaned and recharged air filter (before I cleaned MAF), replaced fuel filter with bigger 3" filter. All of that has been done in the last 6-8k miles.

[Badass_forever]

To me that sounds like a MAF problem. But your IAC could be starting to fail, or the TPS could be getting a dead spot.

Hook up your handheld and watch it when it starts to act up, see what is dipping and intermittently failing possibly.

[HotRaud90]

By handheld, are you referring to a generic OBD II scanner, or my Xcal2? Can the Xcal2 be used to scan for that stuff? Is there any way to tell for sure when the TPS is failing besides scanning for it?

As an update, the car fired right up and regulated to normal RPMs while in park both times I started her today. However, there were a couple times when I shifted in to drive or reverse and the RPMs would dip lower than normal, dippin as low as 600-650. It also continued to have the intermittent delay in throttle that resulted in easing on the gas from a stop only to have the throttle delay and then suddenly spike up in acceleration.

The fact that I fiddled with the throttle body kinda has me wondering if it's the TPS, but that could be just me overly analyzing it since I touched it. Maybe I should clean the throttle body and see if anything changes? Haven't cleaned throttle body since I've owned the car.

Any other thoughts?

[fastblackmerc]

Clean the MAF, IAC and TPS.

[MOTOWN]

You can "clean" the maf , iac and the white walls , more than likely your problem is a bad IAC , you can clean a bad part all day long! Its still going to be bad!

[Krytin]

Is the MAF plugged in all the way - assuming you unplugged it when you removed the tube?

[HotRaud90]

Is the MAF plugged in all the way - assuming you unplugged it when you removed the tube?

Krytin wins! Looks like the MAF wasn't fully seated. Plugged it up, started the car, and let the car adjust to the change. Few seconds of rough idle, up and down from 700-1000 RPMs. Finally it normalized and I gave everything a test drive. Felt smooth again.

I will, however, be checking the TPS and cleaning if necessary. I didn't clean it the last time I did a routine maintenance on things like MAF, IAC, etc.

Thanks all, especially to Krytin for helpin me realize I was lookin right past the obvious

[Badass_forever]

By handheld, are you referring to a generic OBD II scanner, or my Xcal2? Can the Xcal2 be used to scan for that stuff? Is there any way to tell for sure when the TPS is failing besides scanning for it?

As an update, the car fired right up and regulated to normal RPMs while in park both times I started her today. However, there were a couple times when I shifted in to drive or reverse and the RPMs would dip lower than normal, dippin as low as 600-650. It also continued to have the intermittent delay in throttle that resulted in easing on the gas from a stop only to have the throttle delay and then suddenly spike up in acceleration.

The fact that I fiddled with the throttle body kinda has me wondering if it's the TPS, but that could be just me overly analyzing it since I touched it. Maybe I should clean the throttle body and see if anything changes? Haven't cleaned throttle body since I've owned the car.


Any other thoughts?

yes, your xcal2 should work as a scanner as well, download the software from sct and it works as a full scan tool with anything i've connected it too.

I'll link you all the info once i get my laptop from the garage.

also! common, i should get a shout out!

[HotRaud90]

I have the xcal2 software already. I'm aware of what you speak of. I'll know to use it in the future.

Also, a shout out to Mr. Forever for pointing me in the right direction as well

[lifespeed]

I will, however, be checking the TPS and cleaning if necessary. I didn't clean it the last time I did a routine maintenance on things like MAF, IAC, etc.

I don't think there is any value in cleaning a TPS, they are a variable resistor. If they get glitch or a dead spot you replace it.

[HotRaud90]

I don't think there is any value in cleaning a TPS, they are a variable resistor. If they get glitch or a dead spot you replace it.

Noted. I'll keep that in mind.

[Krytin]

Krytin wins! Looks like the MAF wasn't fully seated. Plugged it up, started the car, and let the car adjust to the change. Few seconds of rough idle, up and down from 700-1000 RPMs. Finally it normalized and I gave everything a test drive. Felt smooth again.

I will, however, be checking the TPS and cleaning if necessary. I didn't clean it the last time I did a routine maintenance on things like MAF, IAC, etc.

Thanks all, especially to Krytin for helpin me realize I was lookin right past the obvious

Glad it helped - I learned it the hard way! LOL