Did some work, Now when car is slowing down in gear, sudden drops in rpms...

[tmoneyballin]

Alright, so the day sucked at work, but I was looking forward to tearing up some **** with the cobra...

I did a little playing around and the check engine light came on and I am like F$*% I thought I just paid a lot of money for you to go away!!! I am praying its just a bad O2 sensor, which I will mess around with tomorrow.

what the car is wanting to do is if I am not getting on it - "fake" idle at now 1900 rpms(reset the computer from disconnecting the battery) b4 I tried resetting the computer it would do it add 2,000 even. Some have advised it may go away (I mean I did do a LOT of work at the same time) but what concerns me even more is it will skip rpms when the car is slowing down in gear - it will hit 1900 rpms hold for almost a second and then "release" and decrease normally BUT it seems like around 1600 rpms down to 1200 it will almost skip. It happens mainly when I am in gear slowing down(usually for a light) and it will hit 1900 hold and then skip a couple 100 rpms very quickly when it final returns to idle at 1,000 rpms, which it should really be 900 rpms....but I will take what I can get...

I am wondering if I should keep driving it without getting that code pulled, or if this is just a common problem with your car computer getting acquainted with hella modifications...

The problem seems like the car keeps telling itself that it should idle at 1900 and then will go back to regular idle...with an occasional sudden hicup of a few 100 rpms quickly.

I mean I questioned with my friend whether we could have possibly screwed anything up - like wiring the IMRC module wires to the correct side or each IMRC but reversing it - I am not sure what putting the wires on the wrong side to the IMRC would do anything bad - or even this, but we were pretty careful overall. The other reassuring thing is the car is running VERY fast right now - tires just spin in first 3 gears if I step on the gas at 2,000 rpms!

I am wondering if its just I am not accustomed to the feel of adding an aluminum driveshaft and 430 gears at the same time...

Any advice? All I have gathered so far is the car "should" start to act more normal...but I have had my fair share of mustangs and this seems awkward...

THANKS

 

[ZIncGTSTANG]

Vaccum leak or torn gasket?

 

[tmoneyballin]

No Vaccum leak or torn gasket likely, the gaskets were reusable and very high quality. Replaced most hoses when I put the IMRC module in. The car is running BALLS fast is the scary thing - it took an 03 cobra...I just can't fathom why it is running so weird, maybe its just the computer needs to be adjusted...???

 

[squares98]

You have a custom tune right?

 

[tmoneyballin]

No custom tune since the original WORK about 2 years ago, but these mods all got put on over the course of a week and a half - all of which the car was jacked up and not driven. I know I have to throw some more money to upgrade/fix things potentially, like I filled the antifreeze resevoir completely and I checked it after 20 miles of driving today and it dropped a couple inches! I keep bottled water in my trunk so I had it covered. It is also burning a LOT of oil lately - I had my oil changed about 2,000 miles ago and I just had to add about 4-5 quarts of mobile one to get it to proper levels (It has a canton oil pan ...more oil capacity)

I'll be honest the advice I get here will be very helpful as usual. I also may add that I am willing to spend another $500-$1,000 for other "solid" mods like a chip or something...so if you see an area where I can upgrade to "help" solve the revving problem...I am all ears!

THanks

 

[tmoneyballin]

Would adding a custom chip help fix idle problems in general? I plan on getting the check engine code pulled again which will probably say it is still something with the IMRC's but unless we reversed the wires to each IMRC - we replaced it with a new module. The only other reason that code gets thrown is bad 02 sensors I am told. I assume as far as addressing the potential bad 02 situation do I have to plug and play to find the bad sensor or are they typically obvious or visible? Any insight in replacing 02 sensors as far as throwing codes, etc?

The car is running way to strong for the IMRC's to be potentially malfunctioning - so I am crossing my fingers that it is the 02 sensors.

Thanks for the input in advance...

 

[Kilgore Trout]

This thread sucks because:

-you say you were messing around with the car but fail to say specifically what you were doing
-the check engine light is on but you do not tell us the codes that are being thrown
-you have Cobra issues but are posting in a GT forum
-your sentence and paragraph construction seems to indicate that you spent quite a bit of time on the "short bus"

 

[tmoneyballin]

Yeah you are right, I must have spent a lot of time on the short bus to graduate from one of the top 10 business schools in the NATION - UGA Terry College of Business, with honors. But hey, maybe I am dumb and just make 6 figures because nobody has figured it out yet...

I posted in here, because if you know your **** about "modular" mustangs, you know how a DOHC aka cobra engine works - its not that complicated . More mustang savy people tend to browse the 4.6 forum than the SVT so I can get a quicker response therefore I am more likely to get professional input in this forum. It's simple either you see the title of the thread and you can contribute because you know where I am coming from or you skip over it and don't waste your time.

Sorry you are mad that my car will spank the s%^it out of whatever you have and is not running 100% and can still beat vette's and supercharged mustangs... Thats what 13 grand in your engine gets you...you probably wouldn't know...:Zip2:

Fortunately I will pull the code again which will probably indicate the IMRC (Intake Manifold Runner Control) which I have replaced the module and cleaned the IMRC's but if you have a GT you wouldn't need to concern yourself with that part. The fix in that case will be replacing a bad 02 sensor like I mentioned.

My question pertained to idle issues and inconsistent rpm movements when the car slows down in gear - a very reasonable question and concern.

Unless advised otherwise I will just get a custom chip and keep smoking anything I come across on my side of town. Thanks for the insults though, I kind of feel bad for you...

 

[Kilgore Trout]

I am not sure about all that I could care less about unsubstantiated facts you present about supposed educational credentials, etc... I do also think your choice of username is quite stupid as well...

Anyways I would suggest you describe what you were "messing around with" and post the codes your are getting. AutoZone will pull them for free.

 

[tmoneyballin]

I am heading to the liquor store and then autozone when I get out of work(liquor store is going out of business gotta love 30%+ off of your premium liquors!).

I removed everything down to and including the lower intake manifold - which was removed and I replaced the IMRC module and cleaned the IMRC's. The only room for error here was if we ran/switched the wrong (two lines, one to each IMRC) line to each side of the IMRC's from the IMRC module that is bolted underneath the manifold. We were very careful to make sure we didn't reverse the lines from the original setup, but to be honest nobody has mentioned in any threads to my knowledge what would happen IF we reversed the wires. Plus the car is running WAY too fast for a MAJOR error like that - I can feel the IMRC's actuate at 3,300 rpms so I know they are not stuck closed or opened. The only other culprit like I mentioned for throwing the original code(which I don't have access to right now) was bad 02 sensors, which would also trigger a "bad" IMRC code.

I have an offroad H pipe with MIL eliminators so that shouldn't necessarily throw the code. I also added a cold air intake, aluminum driveshaft, 430 gears and a new fuel injector(one was bad). All the other engine work (forged internals, heads, intake, oil pan) were all done about 2 years ago and shouldn't necessarily cause a sudden problem. I don't think there are any vaccum leaks because we replaced the only two bad hoses and the car does idle around 1,000 rpms which is fairly normal - if there were leaks it wouldn't idle(which was initially the case before we replaced the hoses).

The two problems are the car wants to "pretend" to idle temporarily around 1,900 rpms and also it will "jump" or "skip" from say 1500 rpms to 1200 rpms very roughly when the car is in gear and slowing down on various occasions. It doesn't always happen like clock work, but it does happen randomly and I am just wondering if it's "normal" after you have effectively added a lot more power to your car in one effort - meaning the car was not running for a week and a half while we worked on all the above mentioned mods and the computer is now reading a lot of different changes...

 

[WillDuhhBeast]

Yeah you are right, I must have spent a lot of time on the short bus to graduate from one of the top 10 business schools in the NATION - UGA Terry College of Business, with honors. But hey, maybe I am dumb and just make 6 figures because nobody has figured it out yet...

I posted in here, because if you know your **** about "modular" mustangs, you know how a DOHC aka cobra engine works - its not that complicated . More mustang savy people tend to browse the 4.6 forum than the SVT so I can get a quicker response therefore I am more likely to get professional input in this forum. It's simple either you see the title of the thread and you can contribute because you know where I am coming from or you skip over it and don't waste your time.

Sorry you are mad that my car will spank the s%^it out of whatever you have and is not running 100% and can still beat vette's and supercharged mustangs... Thats what 13 grand in your engine gets you...you probably wouldn't know...:Zip2:

Fortunately I will pull the code again which will probably indicate the IMRC (Intake Manifold Runner Control) which I have replaced the module and cleaned the IMRC's but if you have a GT you wouldn't need to concern yourself with that part. The fix in that case will be replacing a bad 02 sensor like I mentioned.

My question pertained to idle issues and inconsistent rpm movements when the car slows down in gear - a very reasonable question and concern.

Unless advised otherwise I will just get a custom chip and keep smoking anything I come across on my side of town. Thanks for the insults though, I kind of feel bad for you...

If you're making 6 figures, you should buy a new car. Maybe.. a Lotus exige.. or.. the new BMW M3 is pretty sweet. Or if you wanted to go with big displacement.. the new z06.. or even a 4cyl turbo like an Evo or an STI. Thats just my opinion on that..


As far as inconsistant rpm when it idles down in a Cobra.. I have no idea.

Maybe I didn't catch it the first time.. but did you even mention what year it was?

 

[tmoneyballin]

The car is a 98 Cobra, I appreciate the financial perspective on how to "waste" my money - you will find that a car is the worst investment you can make, however my family and I have invested in several condo's in Destin, FL and become millionaires - oh and my dad who is a multi-millionaire drives a 1999 buick century with 150k miles on it - when he could also go out and pay cash for a new SL500, which is personally where I would "waste" my money if I hadn't been raised by smart parents. Don't take it like I am bragging either - my Dad came from a poor family and single handledly made his family a success...something anyone would take pride in.

I replaced the PCV valve and for now the check engine light has gone off because that what the P1506 code usually means. As far as the idle, I may take it to a local shop and get a custome tune/chip burned if it doesn't fix itself. Right now it actually launches the car quicker so that why I am jumpin out on these vette's and cobras.

Took another vette this morning, on the way to breakfast, he gave up by the time I hit fourth. Just one more embarassment for the "good guys".

Thanks for the advice guys.

 

[PlatinumDevil]

If you were raised so smart why are you street racing on the way to work???

Is it possible you reflashed your computer and erased the tune or something? My last car had a custom tune and one day the factory chip fell out of the bridge chip and it acted very erratically but still ran extremely fast. It idled at 2300 and would bog if stepped on and then pick up and run extremely fast again in upper RPMs.

I would take it to a shop and get it checked out if your making 6 figures a year. Unless by 6 figures you mean 6000.
seriously though i imagine its a tune issue or a vaccuum leak somewhere.