Rivven87

I'm getting ready to sell my 87 V6, so I'm trying to get it into a bit better running form.

I'm told it's in limp mode, due to some sensor problem, because for the last couple months it's been really pulling fuel a little sluggish, hard as hell to start when it's hot, and idles high. I don't deal well with fuel injection, but most of that just seems like it's running extremely rich, which I'm also told happens in the limp mode.

The EGR is apparently working, O2 was replaced six months ago to pass the smog test, MAF replaced a bit after that because the throttle was surging at low loads, and I just got done boiling my CTS, because the temperature gauge always reads pretty close to 40 degrees, something I always ignored, but someone suggested I test it. It started at about 1700 ohms and went down to 180 when the water got to a full boil, so it's apparently working.

I'm about out of ideas, but I don't particularly want to sell it running the way it is.

Danno

How does it run above say 35mph on the road. What you need is to isolate where the problem is. Have you scanned for codes? Many FI problems wind up to be very simple. Since it passed a smog test most likely the major parts are not an issue. Based on your complaint I would look at the throttle body first. Pull the IAC and check for heavy deposits on the pintle and inside the TB idle air passages. Many an issue can be solved by simply cleaning the pintle nose and TB. My recommendation is to replace the IAC if it more that 5 yrs old. They get very gummed up and are slow to respond. You mention EGR is OK, how do you know that? The only way is to pull it and inspect the pintle and the manifold. heavy carbon deposits can prevent the valve from operating correctly. EGR puts a 10-16% dilution of exhaust gas into the engine to reduce combustion temp and emission but at idle as low as a 4-5% mix can cause a rich condition that the O2 sensor can't compensate for. Based on the fast idle I would start with the TB first, you might be surprised at what you find.

LnealZ28

Here's some stuff on limp home mode:
https://www.thirdgen.org/techbb2/sho...sor+failure%22

Rivven87

At 35 it runs fine in second, in third it's sitting at about 1500 and it bogs if I try and accelerate.

The IAC is alright, it was a little dirty but not very, after pricing one, I figured cleaning it out should be fine for now. It doesn't constantly idle high, it's just slow to drop below about 1200. The TB air passages I cleaned in the fall out of a certain level of boredom.

The EGR itself is okay, but in a very bad maintenance session this morning I discovered that while the EGR is clean and operates when you give it vacuum, it might not actually be getting any. The EGR vacuum comes off a split on a small cylindrical.. thing. Vacuum goes into the split, but it either doesn't get to the EGR or is so light I can't feel it.

But, this morning I decided to pull the CTS and replace it, after some insistence that it was sending a bad reading since the temp gauge never rose above 45. Now it rises slowly and constantly right up until it pins somewhere above 125, though it doesn't actually overheat and boil over. Water coming into the rad inlet is hot, but not scalding. Switching back to the old CTS didn't change it.

So I've probably found the problem running rich, though solving it is another matter (which is where FI problems are pretty much never easy for me, there are about a dozen parts that I can't even identify, let alone guess how or why they function), and I've managed to create a whole new mysterious problem.

Danno

The split thing is the EGR solenoid. Vacuum is fed in one side and the solenoid allows the other line to get it, but the vehicle must be moving. The EGR ONLY operates above 35 mph and is controlled by the VSS or vehicle speed sensor. You may just have air in the cooling system now causing a different reading. Have you scanned for any codes?

Rivven87

Are EGR's always 35mph?

I'm pretty sure there's no air in the coolant lines, the car ran for close to forty minutes with the rad open after it pulled air through the first time. The heat isn't a steady rise though, it does drop down a few times so I'm mostly blank when it comes to that.

Today I had a shop confirm that my diagnostic system is dead. Up until today I thought maybe I was doing it wrong, but it doesn't show any codes at all, which is why I was doing it the old fashioned way when you're clueless; replacing things that you can't identify.

Danno

EGR operates above 35 mph to about 70 or so. If you see sharp blips in coolant temp it is usually air. If the ECM won't show codes at all then you may have more serious issues. Try cleaning the ALDL connector with contact cleaner then try again. If you don't get even the "12" handshake code you may very well be in limp mode. Another test is let it warm up a little and with the ECM dropped down but connected gently tap on it with your hand, not a heavy tool or you can create problems and see if the engine hesitates or stalls. If it does the ECM is in fact bad and no amount of messing with the engine will make any difference.

LnealZ28

If you're in limp home mode the SES light will flash continuously and the motor will barely run. This is the way it happened for me when my ECM died a few months ago. I barely got her off the road before it loaded up with fuel and died, and it happened pretty quickly. It certainly wouldn't run for an extended period like you describe. If you aren't getting the "12" code three times when jumpering the ALDL, then I'd agree that you could have ECM trouble, although yours will crank up and run so I seriously doubt you're in LHM.
https://www.thirdgen.org/faq/thirdgen.shtml#misc