Hello everyone, this paraphrases the second worst day of my life.

My new-to-me C5Z just took a **** in the middle of my drive to work. Was driving when all of a sudden transmission became useless (no throughput in any gear), so I was rolling, engine started to idle and lose RPM until it stalled out. I pulled into the least busy lane on the highway access road I was on and put the hazards on, wanted to give myself more clues as to what the issue was so I tried to start it. It turned over to 600-700rpm, lost RPM fast (took 2-3 seconds), and then stalled out again. Turned it on again; tried to press gas in neutral to tell whether it was a transmission fault; no reaction to throttle. (As in, pressing the throttle didn't raise RPM or indicate any reaction from the vehicle). This assortment of issues is incredibly confusing for me to understand the issues. The car recently had a "new transmission" put in, and didn't have any issues up until this point except some unnecessarily hard to find gears (which leads me to suspect perhaps they didn't fill the transmission fluid?). The engine issues with the RPM and throttle input are a different situation on their own and have thrown me for a loop. I'm not quite sure as what the next move is, I brought it to a different manufacturer's dealership to get it looked at (as I'm good friends with multiple people there, and therefore trust their diagnostic ability and that they won't up-charge it to hell). If anyone sees any parallel in this issue, please give some information, I'm currently unsure what to do as this has turned from a dream to a nightmare in the blink of an eye. I'm hoping it's something as simple as a sensor but for some reason I find that unlikely. I've already been in contact with a few good mechanic friends over the phone who has given me all sorts of ideas such as alternator issues, throttle position sensors, other sensors, spark plugs, etc., etc.

 

Moved to C5 Tech.

 

1st of all is your eng STOCK ? Please list any mods even a CAI or headers
Sounds like your car went into "limp mode"
Several things can cause a limp mode or a reduced power mode which will make your throttle in active---If you can have someone read all your codes Even if you don't have a check engine light there may be a stored code that is causing the issue
On a stockish engine there should be no reason for a limp mode unless you have a sensor failure--Some sensor codes will produce a limp mode--others not
A MAF code a 02 code a TAC code or an ABS code or traction control code will cause a limp mode Most any auto parts stores will read your codes for FREE then report back

 

First off, thank you for your reply, I'm going to the place where I towed it to later to check the codes, as I was unable to last night. Engine is near bone stock, CAI as you said to mention, and SLP exhaust, other then that it's unmodified. I mean my specialty isn't exactly corvettes so perhaps it might be a stupid question but would limp mode cause all of the problems I mentioned? No transmission reaction, no throttle response, no idle?

 

Since you had no response from trans there could only be 2 things that can happen. Broke rear differential or transmission since you didn't hear any noise you can rule out TT because if it broke you would hear clunking and crushing sound. From my experience this should have nothing to do with the engine problem. But if it did go into limp mode most of the time if the engine is turned off it will reset and start again. But it seems obvious the problem is correlated. JMHO.

Just read again i don't think it went into limp mode because it would idle with a higher than stock idle. Well that's the way my car reacts when it goes into limp mode. it will not shut down.That's why it's called limp mode. Limp it home or to a safe place. LOL

 

I figured it wouldn't be related to the engine as well, as there was no problem with it beforehand, so I agree that the problems are most likely correlated, however, the fact the car wouldn't idle for more than 2-3 seconds before stalling itself off gave me the impression that there might be more going on than meets the eye. With either the differential/transmission, the transmission still works on the output side at least, as it would hold the car in first gear and didn't make the dreaded sound of destruction before this event happened. Differential issues are possible I suppose, however that was also supposedly rebuilt as well.

 

You can check for DTC’s through your DIC...not all DTC’s (codes) illuminate the MIL so you may have something stored to give you some direction !!...video below !!

 

I will read the codes later today when I go to diagnose the car, I suspect it's limp mode in conjunction with some other fault relating to the clutch but I won't know until I check it out later today. Will keep updated.

 

Super !!...since we are dealing with an almost 20 year old car if you CAN afford it I would get your own scan tool...they are fairly inexpensive and it really helps in diagnosis...you’d be like a doctor without a stethoscope around his neck !!...keep us updated !!

 

Sounds like it went into limp mode, no response in rpm from throttle input and erratic idle are symptoms of limp mode. Theres probably a sensor issue related to the throttle body and or CAI.

 

I concur, unfortunately my ride got delayed but I'll upload the codes and probably a quick youtube video for review. Just something I noticed, but I see you're located in Frisco, which is funny because the place it broke down was on SB Dallas Parkway just southbound of the 121 interchange. Funny coincidence. Needless to say I'll probably be picking up a beater in a few days as this has been a wake-up call to buy a beater. Was going to buy one probably in 6 months or so but obviously I've been rushed into it.

 

Got the chance to look at it today, forgot to bring scanner. Had a well acquainted LS friend take a look, said the symptoms seemed to indicate fuel pump failure. Does this make sense as an answer to these problems for you guys? I could definitely see how it would engage limp mode or just make the car cut out, and would make sense why the engine wouldn't hold RPM.

 

You’re going to have to get the codes man. Otherwise we’re just shooting in the dark. How can you expect anyone to diagnose the car over the internet without codes?

 

Will update tomorrow when the shop opens and I can stop by and get a good look at it through and through.

 

You NEVER diagnose based on “symptoms” !!...if you do that you’ll be really firing that parts canon...you can pick up a cheap amp clamp at Harbor Freight if you think it’s a pump and check amperage of the pump !!...will not go into reduced power for a bad pump !!...you still need to check for DTC’s !’

 

Disappointing for you. Hope you get it sorted.

 

Hoping this is something simple so you can get on to enjoying the car. Let us know when you have more info. I will say I'm pretty lost about what you're saying about the transmission's role in all this. You talk about the "unresponsive" transmission. I don't know what you mean...the transmission has no electronics so I'm not sure what you were looking for. It's unlikely that the engine would have electronic failure AND the trans would have mechanical failure at the same time.

 

I agree, I was just trying to give a general description of the onset of the problems, I share the view that the transmission has no role in it as there was no horrible destruction noises when the problem occurred and I was out of gear when it happened, just thought maybe it would provide more background for someone to see if they've had a similar issue. I'm in the same boat however, as I hope it is something simple, just got the car not but a couple of days ago. Knew the car would need some work and to be fair still does need some small touches but I'm coming up fairly close to my budget for getting the car on the road.

 

Maybe talk to the technician to did the pre purchase inspection. They most definitely pulled the codes. Maybe there are history codes in there.