85 245 with LH 2.2 m46 Rough Idle

I have had this issue for a while now: very rough idle, surging, intermittent minor power drops.

Things I've done to correct (or because they needed doing):
New pumps (delphi and bosch after in-tank failed) filters and seals
Intake gasket and injector seals (no change in idle when sprayed)
Timing belt (mechanical set to 0deg, ignition set to 10+)
Air filter (as needed)
IAC cleaned and tested (opens and closes with no hesitation, not dirty)
Flame trap replaced (cleaned periodically, filter replaced when intake gasket)
Engine seals replaced (all front engine seals, valve cover gasket, and oil pan gasket. Slight leak from rear main, but will replace when clutch starts bothering)
Spark plugs (use NGK coppers and gapped periodically to 0.030)
Wires, cap, and rotor (replaced within last 3 years)
Catalytic converter (used bosal $80 cheapie, no issues)
O2 sensor tested for within spec (I forget what it was but sweep should've been like 200 to 1000 ohms I think, it tested at around 350 ohms at AMM)

It runs great when I'm driving, but even when I tip the throttle sitting still I feel slight, a-rhythmic miss. Can stall even after warmed up when idle drops too low. I'm not sure where to go next but it is so much rougher than any I've ever owned (or even the ones I work on that barely drive). Any suggestions?

Disconnect the single black wire on the O2 sensor from the harness and connect a volt meter set on the lowest DC voltage range. The sensor will output a voltage of ~0-1 volt depending on the mixture once the sensor is warm if it's working correctly. A reading closer to 0 volts indicates it's running lean, closer to .9 volts indicates rich. Somewhere around .7 volts is normal with the sensor disconnected. With the sensor connected the reading should fluctuate regularly above and below .5 volts. The sensor may have failed sending incorrect info to the ECU.

It's also possible that you're fuel pressure regulator is failing. Do you have a way of testing fuel pressure?

AMM failures are also common, especially if the air box thermostat has failed. Hot air from the exhaust manifold will eventually cook the AMM.

My AMM seems to operate fine, when I disconnect it the idle drops and it tries to die, but how should I test for proper results? I can test fuel pressure on anything but the LH2.2 setup (without a lot of junctions and T-blocks), but there is no fuel smell of FPR and it holds vacuum from Mightyvac. Airbox T-stat is long gone. Will double check O2 volts and get back to you, thanks!

I waited until T-stat opened and took the following readings from my O2S:

Connected - ~0.18 volts
Disconnected - 0.00

This sensor is in the exhaust manifold. I also had a fairly new bosch sensor in the straight pipe (pulled it off my 93 before I scrapped it) and that one gave me readings around 0.21 (plugged in or disconnected didn't seem to affect the reading). So I guess I need an O2 sensor, but I'm wondering if I didn't wait long enough to get accurate readings considering both sensors didn't give fluctuating signals?

A heated (3 wire) O2 sensor should be warm within a minute or 2. Unheated (1 wire) within 5 minutes. The O2 sensor needs to be grounded so the one laying in the pipe probably wasn't reading correctly.

If the sensor is working you're running lean. Did you verify that the in-tank pump is working? Some of the pumps being sold have the poles reversed.

In tank pump works great. The downstream sensor should be lean anyway (can you say exhaust leak?) past the cat. Already ordered new bosch sensor will post results after install.

Update**

I replaced the O2 sensor (PITA given it was so in the that even once I got it loose and rocked it with heat and PB blaster, it pulled all the threads so I had to use a pick and mirror just to get my thread chaser to grab at all) no noticeable change and the sensor reads about 0.04 VDC on the single wire. That seems way out of range, did I get a bum part, is bosch 13957, or does the antisieze need to dry before it can ground properly?

Any other suggestions?


P.S. I probably should've replaced the sensor after I did my HG, it was full of corrosion!

Update**

After the O2 sensor was replaced, I did spark plugs and fuel filter just in case, all were fine as the had been done less than 8k miles ago, no loss. Then decided to check my valve lash (hadn't adjusted since new cam was put in) and of course two of the eight that needed changing initially required another adjustment (been collecting from JY for years now). That helped a lot of the shaking, but it's still not where I want it.

When I disconnect MAF, O2 sensor single-wire reads 0.95, reconnect and it wobbles all over the place usually 0.3 to 0.7 VDC, is this where I want it? Should I adjust fuel screw, or is this normal?

You are seeing the o2 sensor oscillate around the proper voltage reference. That .3 to .7 range is perfect for a reference.

Glad to hear, I will say she is driving much better after I did all of the above and sprayed the AMM clean. The thing that really bothers me though is that there is an arhythmic miss at idle and at all engine speeds below 2000 rpms. I otherwise it's got plenty of power throughout the range (thank you VX cam) and does great on mileage (26 mixed driving) when I'm not pushing her even with A/C on. Any thoughts on the miss? I did the HG 10k miles ago, no burnt valves and I still had that miss then if a bit more pronounced...

How about your spark plug wires, particularly the coil wire? You say in the first post they were changed 3 years ago, but were they good quality?

I had a nagging problem with irregular ignition; changing the wires solved the problem. Disclaimer: a lot of other parts were also changed as well; it could have been that changing the wires was the final piece of a multi part puzzle.

If you're in the salt belt. Plug wires only last about three years nowadays. That brine just makes insulation fail. The coil wire has failed more often than the engine wires in my 93 wagon.

Yea, wires are visually good and coil wire has 7.5k Ohms. I'm in the sun belt but she came from the land o' Salt, though everything has been replaced since...I have been wanting some bougicord replacements but have been too cheap, maybe now is the time to bite the bullet just to rule everything out. Current set are decent Delcos with really nice insulation around the plug but I'm not ruling anything out. Thanks for the input!

Plug wire spec for the carbon core wires is 500 ohms per foot. So, a 7.5k ohm coil wire seems a bit high. I recommend the wire wound mag core wires. They work really well and you can get them for less than a set of bougicords on Rock auto. I've bought mag core wires there for as cheap as $16 a set.

Ok, will order a set and report the results. Thanks for the advice!

New wires on: the miss in mid-high RPMs is gone, but the idle is still rougher than I'm used to. It hovers ~850-950 rpm I can't get it any lower even with adjusting thumb screw and throttle cable. It's getting better with each upgrade (luckily), but still not ideal...

I'm happy with the performance, but would love some advice for smoothing out this idle, thanks in advance!

Have you adjusted the valves? Another good check is to make sure the throttle body is clean and closing properly. There is a spec for the idle speed with the air bypass closed. I think it's 750rpm.

dl242gt said:

Have you adjusted the valves? Another good check is to make sure the throttle body is clean and closing properly. There is a spec for the idle speed with the air bypass closed. I think it's 750rpm.

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As stated above, valves have been adjusted, cleaned and inspected TB around 10k miles ago, but will check again. Thanks