Car not running right(long)

my85grandnation

85 Triple Threat
Ever since its gotten cold here this year in Colorado my hotair has been acting up. I drove this car last winter and did not have this problem. When I start it up after its been sitting over night or after work it seems like its not running on all 6 cylinders. Once it warms up it seems ok but while your driving it every once and a while it will kind of act like it has a miss and stumble. This only appears to happen around 1800 RPMs. If I jump on it though it wont miss a beat. Then when I come to a stop light it will sit and stumble a bit. It is an all stock car with only the chip being an upgrade as well as a stock location K&N. Has a little over 100k miles on it. I dont have a scantool so I dont have any#'s or stats. I have no idea what it could be since Im still fairly new with these cars. Please let me know what you think I should check. Thanks

Dusty
 
my85grandnation said:
Ever since its gotten cold here this year in Colorado my hotair has been acting up. I drove this car last winter and did not have this problem. When I start it up after its been sitting over night or after work it seems like its not running on all 6 cylinders. Once it warms up it seems ok but while your driving it every once and a while it will kind of act like it has a miss and stumble. This only appears to happen around 1800 RPMs. If I jump on it though it wont miss a beat. Then when I come to a stop light it will sit and stumble a bit. It is an all stock car with only the chip being an upgrade as well as a stock location K&N. Has a little over 100k miles on it. I dont have a scantool so I dont have any#'s or stats. I have no idea what it could be since Im still fairly new with these cars. Please let me know what you think I should check. Thanks

Dusty
Without basic information like IAC, MAF and O2 numbers, it is difficult to offer meaningful help but you sound desperate. Let's focus on what is common or what can be checked visually. You mention that after sitting over night or after work that car sounds like it is not running on all cylinders. You may have an injector leaking down. If so, fuel will drain into a cylinder and cause a horrible start up. After 10 to 20 seconds, will clear up and run normal. If you have a guage on your fuel rail, see how long it takes for pressure to fall. Do not know the official time frame for normal gradual reduction in fuel pressure but would say that a drop to 0 psig in less than 5 minutes is an indicator.

Other basic checks and cleaning are as follows.

- Check intake hose for leaks.
- Clean IAC motor (tapered head and seat).
- Clean air cleaner (should be able to get the cleaner & oil from Advance, Autozone, etc.).
- Replace vacuum hoses (primarily near high heat areas like turbo). Feel for scammer sections.
- Replace PCV valve (OEM)
- Check TPS. Assuming same values as 86 & 87 models, .42 to .48 volts at idle and greater than 4.6 volts at wide open.

For your Christmas, recommend having a scan tool like the Scanmaster on your list. Till then, hope this helps.

Richard
 
You can take a look at the spark plugs to see if they are even in color. The problems is that the ECM tries to even out the cylinders A/F mixture when running. So, a rich injector looks on it's spark plug, but the others will look lean.

Yet, leaking injectors at engine off will leave a rich looking pattern in that cylinder's plug.

You can also call up the codes from the ECM. Clearing the ECM may not be a bad idea. Cleaning the fuel injectors is also a good idea. Some pour in type of additive should work.
 
Well I dont have a check engine light so I dont think its throwing any codes yet. I also tried running some BG 44K thru it which usually helps any of my cars when injectors are dirty. It takes more than a few seconds after start up for it to act like its on all cylinders. I was thinking maybe the problem could be a combination of old plugs and old plug wires since its not a constant problem. I know that when a plug wire goes bad that sometimes it will work and other times it will make it miss a bit, and a bad wire could explain why its only at low RPM's where the coils not firing as much power thru the wire so if its got resistance then the affect is greater than at full throttle when there is more power going thru the wire. I went and got new plugs and wires tonight and will put them on and see what happens.
 
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