rough idle

supercoupe95

Registered User
i have a 95 sc (auto) with about 85000 miles and when the engine warms up it runs really rough and sometimes dies like if im at a stoplight or backing up. as soon ad i hit the gas to take off it runs fine, also the tach drops when i get to about 4000rpm's. anybody have a clue what might be wrong
 
I don't know about the 4K rpm drop, but as far as idling rough, check your engine mounts. Mine did the same thing you're describing. I changed the mounts and all was good to go. Take care.
 
vacuum leak

check for vacuum leaks . how is the vacuum at idle should be about 18 idling .look for hoses that may have been bumped during recent work under the hood?
 
I have a similar problem. When my car starts cold, it losses vacuum, runs rough and dies until it warms up. Also, when I am at a stoplight for a period of time my car will die.

Could this also be the TPS or IAC?
 
my 95 idles at around 500 warm...but the issue i have is that at idle in park vaccum sits at 20 which is normal..but when put into gear it drops all the way to 10 ....iac is good, maf good...what about tps how to test?..or any other ideas, car never dies and runs fine
 
Motor mount test

supercoupe95 said:
i was wondering how you check your motor mounts?
An easy way is to have someone to sit in the car with your foot on the brake and put the car in drive and then in reverse.
Watch the engine to see if it rises up. You may also hear a clunk.
From there you can look to see which mount failed.
The drivers mount on my SC was toast and the passemger mount actually looked good. I replaced both of them anyway.
You can also tell if your mounts are collapsed if you don't have any clearance between the oil pan and the cradle.
Your oil filter will be a real pain to remove if your mounts are collapsed.
As for your bad idle you may have a vacuum leak.
What does your gauge say at idle in park and in drive?
Bill
 
my idle in park is 20, put in a gear it drops to 10????




blue94sc said:
An easy way is to have someone to sit in the car with your foot on the brake and put the car in drive and then in reverse.
Watch the engine to see if it rises up. You may also hear a clunk.
From there you can look to see which mount failed.
The drivers mount on my SC was toast and the passemger mount actually looked good. I replaced both of them anyway.
You can also tell if your mounts are collapsed if you don't have any clearance between the oil pan and the cradle.
Your oil filter will be a real pain to remove if your mounts are collapsed.
As for your bad idle you may have a vacuum leak.
What does your gauge say at idle in park and in drive?
Bill
 
I have had the same issue with my 94 for a year and have read every "rough idle" post hoping the silver bullet fix had been found. The SC has 100,000 miles on it now with a fresh long block at 65,000 miles. I bought it with 73,000 miles. I replaced every module and sensor and as many of you know it ain't cheap. Obviously, I'm still missing something. I have solid mounts and removed all of the vacuum hoses to eliminate vacuum leaks with no luck. I have teflon IC gasksts and sprayed carb cleaner to ensure no leaks. I replaced the fuel injectors (only takes me 2 hours to do the whole job now) and matched MAF tubes. I contacted C&L and they agreed my setup was right. I have an ACTRON code scanner and ran the cylinder balance test yesterday. Cylinders 4 & 5 failed. I ran the test again and cylinder 4 failed. I ran one more time and it passed. Shut the car off and let sit for 20 mintues and ran the test again. Cylinders 4 & 5 failed. I'm not sure what it does doing this test. I don't know if the fuel is shut off or the spark is interupted. Anyway, I swaped coils between my 90 XR7 and the 94. No joy. I pulled the battery cables off to reset the computer and let it learn the changes with no luck. I just installed new wires and iridium plugs. No joy. I even bought an MSD DIS-4 ignition box and the 2 required adapters hoping that would make a difference. It did not. Mine now has the added feature that when I accelerate from a stop it is very slow to respond especially with the AC on and then takes off. I have to almost mash the gas pedal to get it to go. It appears to run good on the road at 50 to 70 MPH but I get terrible gas mileage. Around 10-12 MPG. The real frustrating thing is I never get a hard CEL to tell me what is wrong. I do get a momentary CEL sometimes when I'm climbing a hill in OD but as soon as I get on level raod, the CEL goes out. The code does not latch so I'm back to square 1 with diagnostics. So as you can see I'm really enjoying my SC. Right! I would be one happy camper if the 94 ran as strong as the XR7. And that is the other frustrating thing. I did the same mods on my XR7 as the 94 and the XR7 runs really strong. The only 2 primary differences between the two setups is different trannys and different ignitions.

Still searching for the silver bullet fix!

Ed Springer

90 Black XR7 5-speed: 70mm TB, Fresh Air Intake, '94 Supercharger, 5% SC Pulley, Raised SC Top, I/C Fan, UD Pulleys, 190 l/h Fuel Pump, 36 lbs Injectors, Headers, Magnaflow Muffler (no cats) with stock resonators, 3:27 Gears, Ripper Shifter, 73mm CL MAF (Blue Tube), Magnacore Wires, NGK Iridium Plugs, Royal Purple Lubricants and Rear Spring Air Bags.

94 Red SC Auto: 70mm TB, Fresh Air Intake, Stock 90 SC Pulley, Raised SC Top, I/C Fan, 190 l/h Fuel Pump, Headers, Raven Muffler (no cats) with stock resonators, 3:73 Gears, Accel 36# injectors, 76mm CL MAF (Gold Tube), Magnacore Wires, NGK Iridium Plugs, Royal Purple Lubricants, TRANSGO Shift Kit, Pro-Torque 2500 Stall TC, Haydon Auxiliary Transmission Cooler, Tokico Struts & Shocks, American Racing 17” Sniper Wheels, Michelin Pilot Sport A/S Tires and 235 RWHP with 315 LB-FT Torque.
 
i know that someone on this post did not say that engine mounts were the cause of rough idle....look if you dont know what youre talking about just dont bother...theres only so many things: vacuum leak, clogged injectors/bad injector, some kind of emissions equipment problem, cam or crank sensor, or at the worst a worn lobe on the cam....
 
Normal

rzibilske77 said:
my idle in park is 20, put in a gear it drops to 10????

From what you are describing your idle in gear is pretty normal around 18-20 in neutral and almost half that in gear at a stop sign, so it doesn't sound like a vacuum issue.


Try unplugging the IAC while it is running....., it should die, if not I would suspect the IAC is causing the rough idle especially if it is the original and has never been replaced.


Smitty
 
rzibilske77 said:
my 95 idles at around 500 warm...but the issue i have is that at idle in park vaccum sits at 20 which is normal..but when put into gear it drops all the way to 10 ....iac is good, maf good...what about tps how to test?..or any other ideas, car never dies and runs fine

TPS just sends a signal to the EEC telling it what position it is in. Not very likely to cause rough idle , although anything is possible.

How do you know IAC and MAF are good, what did you do to test them both? Just wondering.

Smitty
 
sclovehater said:
i know that someone on this post did not say that engine mounts were the cause of rough idle....look if you dont know what youre talking about just dont bother...theres only so many things: vacuum leak, clogged injectors/bad injector, some kind of emissions equipment problem, cam or crank sensor, or at the worst a worn lobe on the cam....

It's really not necessary to get yer shorts in a knot. :rolleyes: I have read on here a few different times where people have installed new mounts and other, seemingly, unrelated problems cleared up. Why? Don't know. Does it make sense? Not to me. The point is, someone asked for help and advice. He has obviously checked most everything else so who knows.... But jumping in and throwing an attitude does not help anyone track down or solve a problem. :rolleyes: What helps is for people to politely pass on information about what has worked for them in the past.

supercoupe95 said:
i have a 95 sc (auto) with about 85000 miles and when the engine warms up it runs really rough and sometimes dies like if im at a stoplight or backing up. as soon ad i hit the gas to take off it runs fine, also the tach drops when i get to about 4000rpm's. anybody have a clue what might be wrong

What exactly do you mean by "-the tach drops off"? Is it just the tach that drops or does the engine actually die off too? If it is JUST the tach dropping and not showing true engine RPMs, then you may want to check out the Cam Sensor. And ya never know, it could be yer engine mounts too. :D :D

Tracy
 
XR7inWI said:
... not necessary to get yer shorts in a knot. :rolleyes: I have read on here ... people have installed new mounts and other, seemingly, unrelated problems cleared up ... The point is, someone asked for help and advice. He has obviously checked most everything else so who knows ... But jumping in and throwing an attitude does not help anyone track down or solve a problem. :rolleyes: What helps is for people to politely pass on information about what has worked for them in the past ... And ya never know, it could be yer engine mounts too. :D :D

Thanks Tracy. I wanted to come back and say basically the same thing to the hater, but I didn't want to get in a shouting match. I knew it would have come to that. We aren't here for that. We're here to help each other.
 
I found my silver bullit fix!

Just thought I would pass on what I finally found to fix my severe rough idle problem as described in my above post. Replaced 4 burnt exhaust valves. Finally did a compression test. Don't know why I did not do it earlier. Thought it was HGs but they were perfect. Replaced all the exhaust valves, valve guides, resurfaced all the valve seats, resurfaced the heads, upgraded to ARP head studs and Scorpian 1.73 roller rockers. Put her back together and all is well.

Hope the guy with the bad TUDE gets a grip!

Ed Springer

94 Red SC Auto: 70mm TB, Fresh Air Intake, Stock 90 SC Pulley, Accel 36# injectors, Scorpian 1.73 Rockers, ARP Head Studs, 190 l/h fuel pump, 180° Stat, Raised SC Top, I/C Fan, Headers, Raven Muffler (no cats) with stock resonators, 3:73 Gears, 76 C&L MAF (Gold Tube), Magnacore Wires, NGK Iridium Plugs, MSD Ignition, TRANSGO Shift Kit, Haydon Auxiliary Transmission Cooler, ProTorque 2500 TC, Tokico Struts & Shocks, Royal Purple Synthetic Lubricants, Optima Yellow Top Battery, American Racing 17” Sniper Wheels, Michelin Pilot Sport A/S.
 
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