305RSlc

Ok guys, here's the deal. I just started driving my car about 4 days ago. At first, it had an aweful idle at around 2500rpm on start up. Well it turned out to be the upper plenum to runner gaskets was leaking. I had attempted to set the idle speed with this condition and ovbiously it wasn't the best job. Well, after gettting the vaccum leak fixed, I figured I'd set the idle speed correctly. I did the proceedures as outlined in numerous posts, and got it to idle at 650 in DRIVE at operating temp (I have a 91 L98, auto) However, the idle is rather rough, not terrible, but not smooth by any means. It is sometimes jerky when going up hills in 4th gear, like it's struggling as well. I have already replaced the cap, rotor, O2 sensor, have bosch platinum plugs (gapped at .035"), accel 8mm wires. My car also has smog delete, longtubes and 2 1/2" true duals. I am having trouble figuring out what could cause a rough idle on my car since most of my ignition stuff is new. Should I check the coil? How does CTS affect idle, or does it? Could an old fuel filter cause this? Could low fuel pressure cause it? The car does have a SLIGHT rich smell in the exhuast, barely noticable, but it's there nonetheless. My TPS voltage is right around .53 at idle. could anyone throw out some suggestions as to what to check for making my idle, and driving a bit more desireable. This symtom happens usually below 1200 rpm. Above that it runs smoothly. Timing maybe? Any advice would be appreciated.

305RSlc

Any suggestions? After driving around this evening, the idle got progressively worse. Also, the rich smell got stronger and stronger and it almost smells like raw fuel is in the engine bay now. I am going to check the O2 sensor voltage sometime tomorrow and check to see if the FPR is leaking or something. Other than that, any ideas what I should check for?

Vader

305,

I'll try to reply as best I can, but maybe not in any particular order.

You can test the coil for winding resistance and insulation resistance just to be certain it is good, but if the engine runs well at higher RPM, I would suspect the coil and most of the ignition system is functioning properly - despite the Bosch plugs. The task of the ignition system is easiest at low RPM, and gets more difficult as RPM increases, so your description more or less indicates that it is not causing the idle problems.

The CTS simply reports engine temperature to the ECM. The ECM reacts by adjusting the target idle, operating fans, adjusting enrichment, holding off the TCC, and other various functions. As long as there is no MIL on the dash indicating a problem, the CTS is likely O.K. You can measure the CTS resistance at a known coolant temperature just to be sure it is working correctly.



Yes. A fuel filter that is clogging might affect pressure, which would tend to cause a lean idle condition. This can create poor and uneven power production and result in a rough idle. However, since there is apparently adequate fuel pressure and flow to operate teh engine at higher RPM, this is not likely.

Yes (see above). The only way to be certain is to test the pressure.

That could be an indication of a leaking injector, leaking fuel pressure regulator, high fuel pressure, of faulty oxygen sensor. This somewhat further negates the theory of a clogged filter or low fuel pressure.

Timing at idle should not affect mixture and idle quality unless it is grossly misadjusted.

If the meter is calibrated correctly, that TPS voltage is ideal. Don't even give that a second thought.

The fact that it seems to be running acceptably at higher RPM can indicate a fuel mixture or delivery problem. Injectors that do not create a regular conical spray pattern, but spray in a stream can cause puddling, rich idle, and poor idle. Injectors that do not flow equally will do the same thing. If you do not solve the problem with your FPR and oxygen sensor tests, and new (regular) spark plugs do not help, consider performing a power balance test of the injectors.

TA

iTrader: (1)

I had a similar problem on a TBI car after the water pump comitted suicide and sprayed the engine compartment with rusty water. The connector on the coolant temp sensor was having trouble getting a clean connection through the rust, and was telling the ecm that the engine was ice cold. The sensor was actually fine, but the connection resulted in the ECM dumping fuel through the throttle body in massive amounts. Are you getting any codes on your ecm?

Troy
So Cal

Morley

I had the exact same symptoms when I tried these plugs 14+ years ago, they are junk IMHO. I changed them out with AC's and that problem never came back.

305RSlc

That's kinda what I was thinking too. I did a tune up on the car a while back and used AC's and it idled fine. When I installed my headers, I needed shorter plugs to clear, and to actually install, so I went to Autozone and asked for shorty plugs and the guy looked at me like I was asking him to dig up his great grandmother's grave. So, he went and sized up the platinums and they were a little shorter to clear my headers. Do you have a part number for shorty plugs, or ones that are of decent quality that are a bit shorter to clear my headers?


Vader, thanks for all the suggestions and info as far as my questioning goes. After doing some research, I was beginning to lead towards bad injectors since my car has 150K miles on it and I know those are stock since the previous owner(s) abused and neglected the car. I have a question though. If I were to buy, or make, an AFPR and get the injectors from SLP that are $99.00, could I set my pressure a little lower (since they are 25#) and not have any issues with idle or drivability? I ask because I am not completely into chip burning yet, and ovbiously on a budget, so 100 bucks for new injectors is not a bad deal.

http://www.slponline.com/browse_list.asp

Thanks for the replies you guys.

Morley

Accel makes header plugs. I've used their U groove plugs in the past, they were no better than AC's, and no worse either.

305RSlc

you don't by any chance have a part number do you? Or simply a link to the plugs?

Well, I drove my car this morning and of course, it ran as described in the original post. So I pulled out my"old" AC Delco plugs and changed the 1,3,7, 2,4, and 8 cylinder plugs. The other two are the ones that are a bit tight when it comes to getting regular size plugs on. Anyways, it idled smoother; not amazingly, but much more noticable than before. It drove a bit better too except for in OD. Once i hit about 40-42mph and it shifts into OD and the rpms fall, it kinda stuttered like it used too. It didn't do it nearly as much as before the delco plugs, but it's still a little jumpy. There's a hill on my way to work that I usually try and hold it right at the brink of OD so the rpm are at the lowest and I'll see if it feels any smoother than before. I plan on testing my O2 voltage and fuel pressure sometime this week, hopefully.

Morley

Accel P/N: 8198

305RSlc

Thanks, Morley.