JMSpeed

iTrader: (1)

So I come home from vacation after two weeks and find that the car now idles high and bounces between 1200 and 2200 RPMS on certain instances.

Car Background
I have RTP's and an HR y-pipe for exhaust mods, and a K&N drop-in for intake mods. All of which done before the 75k mile mark. The car is a 2006 manual with 116k miles. Oil was changed at 114k, spark plugs at 105k. I also did half and half Seafoam in the gas and through a manifold vacuum line before putting in the new plugs at 105k. At 110k I changed the power steering fluid via the turkey baster method. I also have an 18" square setup for wheels and tires on Bilstein/Eibach springs and shocks.

I just went through this site for all the ECU reset procedures: http://www.technosquareinc.com/350reset.htm

I have no CEL's at the moment, though one existed previously for the RTP's.

Issue
I start the car and it sits at idle around 1800 RPMs. This issue persists even after warming up. I start driving the car and when I let of the gas in neutral to switch gears, the car auto-blips slightly before the RPMs begin to fall as normal. This happens on every gear change. If I leave the car in gear and let off the gas, the car jerks moderately into deceleration, but then decels normally. Best way to describe it is a hiccup. If I hover slightly between accel and decel, the car bucks moderately between both.

Now, when no gear is selected and I go into neutral, the RPMs fall far enough to be near idle, then will bounce between 1200 and 2200 several times before returning to 1800 RPMs. Occasionally, the RPMs will slowly rise close enough to 2000 before dropping to 1500 and coming back up to 1800.

If I have a gear selected and go into neutral, the RPM's fall to near idle then bounce consistently between 1200 and 2200 until I remove the gear selection and it hovers to 1800.

zakmartin

Assuming the problems didn't start right after you SeaFoamed your car and you're not running on old gas, you might want to start by cleaning your MAF sensor. That's simple and cheap and if it's never been cleaned, now would be a good time.

Hook your car up to a live scan tool and run it through the full warm-up cycle. Check to make sure that everything checks out. If you don't know what to look for, take it to a shop.

If you've got a decent grasp on engine diagnosis, look at the Short Term Fuel Trim (STFT) and Long Term Fuel Trim (LTFT) values after you've gone into closed loop. The normal range is +/- 8. If you're getting +10 or higher for STFT and LTFT, then the engine's running lean. If you rev the engine to 1500 to 2000 rpm and hold it for a minute, and the STFT value drops back down to a more normal reading, then the engine has a vacuum leak at idle. If the STFT value does not change by much, then the lean fuel condition is more likely a fuel delivery problem (i.e., weak fuel pump, dirty fuel injectors or a leaky fuel pressure regulator) instead of a vacuum leak. This can at least help you narrow down your idle issue.

JMSpeed

iTrader: (1)

Good thoughts, thank you.

I'll fill up the gas tank and clean the maf to see if either of those solve the problem. Oddly enough, on the way home the car threw an oxygen sensor code for the pipes and code P0507 for the high idle.

I don't have access to a live scan tool, but I'm tech savvy and handy. Is this an affordable peice of equipment compared to taking it to a shop?

KingOfSneakEr

My Z does something similar. A lot of times when I start it up, it will idle and get stuck at roughly 2800 rpm. Sometimes it will not bounce back and sometimes it will. During a cruise the tach will bounce all over the place.

Oddly enough, if it is stuck at that 2800 rpm position, I can hit my gauge cluster and it will break loose. But it will still bounce and soon go right back to the same position.

I hope we can find a solution to this. I have changed my spark plugs, removed the gauge cluster, checked fuses and nothing. I have not tried to clean the MAF so I will try that as well.

zakmartin

The price will vary according to what you want. You can get a Bluetooth or Wi-Fi OBDII reader and an app with limited live data functions for under $100 (I haven't had to shop for a new scan tool in a while, so check Google to see what's the latest and greatest.)

My personal opinion is that if you want to get the most bang for the buck on a tool that will stay relevant with future updates, spend around $250 and get the Innova 3160 or the Autel MD-802 (which is the one I use when I don't want to hook the car up to my laptop with the AutoEnginuity set-up). A quality scan tool will pay for itself after a few uses. Feel free to check Craigslist for used scan tools. A lot of people will use their scan tool once, get frustrated because there's an actual learning curve, and then sell it at a big discount.

All of that being said, once you go ballz-out on diagnostic tools, you can fill up a tool cart (I have) and spend thousands and thousand of dollars on specialty diagnostic equipment (I've done that too.) Hell, a decent bi-directional scan tool with scope functions can set you back several thousand$ easy. For basic diagnosis, though, I'd stick with the best live data scan tool you can get for under $300.

EDIT:

Forgot to mention, the P0507 code points to a vacuum leak, possible bad IAC or dirty throttle... maybe a bad PCV. It's probably a good time to replace your PCV anyway. Don't screw with your throttle unless you absolutely know what you're doing. You can royally screw up your engine if you start messing with your throttle *****-nilly.

zakmartin

While I'm thinking about it, what's the condition of your battery? If you have heavy corrosion at the terminals, it could put an extra load on your alternator.