Connect a scan tool, verify EVERY sensor and all the computer outputs, especially electronic spark advance and the IAC system.

How old are the usual "tune-up" items--cap, rotor, plug wires, spark plugs?

What is the fuel pressure at prime, and under load?

So i think i figured it out. Tested the tps sensor. The value is supposed to be .525 dc. Well it was set almost perfect at .527 only problem is when manually pressing the throttle the values dont change. It stays at .527, its supposed to change right? Im curious though if the values never changed wouldnt the car run like crap? Car ran pretty well other than the surge here and there.

Did you test the sensor independently, or with a scan tool? The scan tool is much preferred.

Sounds like you found "a" problem, even if it isn't "the" problem. Fix the TPS, see what happens on the test-drive.

Yes, "Generally" .5V with the throttle closed, and 4.5V at WOT. Isn't that about right Schurkey?

If it is consistently 100% inop., then yes, it would run like crap. Among other things, you can think of the TPS like the accelerator pump in a carb'd car. Without it, the computer does not know the throttle has opened (or will be slow to realize it), so it cannot provide fuel enrichment (like the accelerator pump shot would with a carb). A lean hesitation or backfire can be the result.

I'm not Schurkey, but ^that^ is right on. The TPS is important, but don't "Critically precise"; ~.5v to ~4.5v is better than good enough -don't sweat the .525v stuff...doesn't matter. The important thing is that you see a smooth voltage increase when applying throttle...which OP, you're saying that it doesn't do. So...that's a problem that needs fixing, for sure.


I also agree with Schurkey's question about the fuel pressure. Marginal, to poor fuel pressure is a common problem on this engine/car. Probably the second most common problem after vacuum leaks.

Im an idiot. I had tested the tps sensor wrong. Took my a** back out the the garage and tested it the right way and seems to be working although i think it might be on its way out. I made an adpater to test the tps sensor real time while the car is running and every once and a while while it surges the values would move up and down by it self.

Went ahead and bought new tps, gonna try it out after work. See what happens.

This is why I dislike folks testing sensors with a multimeter. It takes ten times as long and gives potentially inaccurate results, and always incomplete results.

You'd not have had that problem if you'd used a scan tool, AND you'd have confirmed the wiring harness all the way back to the computer, PLUS that section of the computer itself.

And in the time it took to check one sensor, you could have verified ALL of them, and their wire harnesses.

Dicking with a computer-controlled vehicle and not being able to communicate directly with the computer is two steps away from hopeless.

If you're going to "hobby" with these cars, you gotta get a decent scan tool that does a data stream so you can see what's going on.

New tps seem to have eliminated the surging. Gonna drive it around a few days before i consider it fixed.

Sorry to jump in. I'm getting a similar issue as well. Is there a scan tool that you recommend?

Any scan tool that does OBD I, and can give you a data stream.

I have an OTC monitor 4000e, and it works really well. You can get 'em on ebay w/cartridges for <$200.

When it was my money, I bought a Snap-On Solus Pro used, from a seller on eBay. I would rather have a used-but-usable Professional-grade scan tool than a brand-new consumer-grade tool.

This was prior to Bideninflation. $350 shipped to my door, including the scan tool, user manuals on DVD, a rechargeable battery with some life left in it, and a battery charger. Including an OBD2 connector with a heap of Personality Keys, and maybe a dozen OBD1 connectors, all of this housed in a bigass plastic "suitcase" for storage. A comparable unit today is probably ~$500, but who knows what deals lurk on eBay?

The software version is 8.2 (2008, 2nd Quarter) which handles domestic vehicles from 1980 1/2 to 2007, and Asian vehicles from "about" that same time period. There's some Euro coverage as well. Depending on the vehicle, I have access to engine, transmission, instrument cluster, ABS, air bags, body computer, etc. My single disappointment is that I cannot auto-bleed the ABS on my '97 K2500. I have access to the ABS data stream, but not the auto-bleed procedure. This was fixed some time prior to the 14.2 software revision--perhaps in the 10.x revision, but I've only heard rumors, I haven't used that version.

Be sure to buy a tool having a software version new enough to cover any vehicles you'd want to use it on, because there are NO upgrades, NO repairs, NO official support at all. Snap-On ended support for the Solus Pro years ago, and the Solus (no suffix) years before that. The somewhat newer Solus Ultra has probably no support by now. Solus Edge, and Solus Legend (the current version) are new enough that Snappy still cares about them.

A scan tool that can provide graphing capability is significantly more useful than one that displays only text.

There are competing professional-grade products from other manufacturers; and there are connector-cable (or dongle) plus software to run on a laptop computer, but I have zero experience with any but the Snap-On scan tools in the last 30-ish years.

I do not know why my reply vanished. The Crossfires are notorious for balance issues between the TBI units. People monkey with the linkages, when often the real issue is throttle shaft wear and or IACs that get weak or dirty. The ECM controls the IACs in parallel and is blind to their physical position, often resulting in the IAC flows to become unbalanced as well.

No. "Notorious" is hyperbole.

The IAC's bottom out every time the veh goes above 30 or 35 mph...just like most other GM IAC's of the era. Thus, the ECM "knows" their physical position as well as any 80's car "knows" it's IAC position.

TB sync is neither a "notorious" CFI problem, nor problematic -even if they ARE slightly out of sync. Throttle shaft bores can wear, but it's also neither a common issue, or especially problematic, or unique to the CFI. In fact, the 1bbl TB unit has a much larger "bearing" surface area, than a TPI throttle shaft has....and a smaller plate area to push against (less force acting on the shaft). To wit, mine had over 150k when I sold it....and it wasn't afflicted w/any discernible TB shaft wear issues at all. OP should start with the actual CFI common issues; fuel pressure, vacuum leaks.

I have no idea why your reply disappeared. I saw it earlier. Site has been acting a little weird for me today. My avatar picture has disappeared along with the avatar pictures for many other members too. Then sometimes I see them and then don't. The only member in this thread that has an avatar picture I can see is DynoDave43. Everyone else just has a colored circle with an upper or lower case letter of the first letter of their member name.

One more thing we will just have to agree to disagree on.

My advice to the first poster is to ignore the BS above.

The IACs do bottom out at times, but then they open back up. The passageways get cruded up, the IAC pintles move on threaded shafts that also gunk up. They get sticky and fail to respond correctly. The IACs get unbalanced as soon as the ECM commands them to open the first time after closing them. The IAC is a vacuum leak and throttle bodies that are out of synch will compound the problem. If you want it to idle correctly it needs properly functioning IACs and properly balanced throttle bodies. These Crossfires will idle so smoothly with the stock cam you can barely tell they running when everything is properly functioning and balanced. Another common issue is mixing up the injectors or wrong injectors installed all together. The TBI units operate at a split pressure and the injectors have staggered flow. I prefer to parallel plumb the TBI units, dummy out the regulators, use a single regulator on the return and install injectors with matching flow rates as that corrects another issue that develops and causes un-even air/fuel ratios between the banks as the system ages.

I have owned a vehicle with factory Crossfire as well as a swapped one. Both ran and idled seamlessly smooth, even the one with a mild cam upgrade. I still have the home built manometer I used to balance the TBI units. If you want it to idle correctly and run correctly, the TBI units must be in sync, the IACs need to be properly functioning, clean and the passageways clean and the injectors need to flow equally which is nearly impossible with aged OE regulators and the stock fuel plumbing. It took me several months of messing around before I finally took a dive and balanced the system out, parallel plumbed it and fitted it with cleaned and flow matched OE GM 9C1 65# injectors, making it actually run better than new.

The throttle shafts will also wear and cause a vacuum leak, want proof, spray a little B12 around them with the engine idling. I had to rebrush both pair I owned that had less than 150K on them. I rebrush low mileage TBIs and Q-Jets as well on both primaries and secondary throttle shafts, they leaked from day one just like the Crossfires. I own the ream and have plenty of the bushings, so I just do them all. It eliminates small but noticeable vacuum leaks.

How many CFI cars have you had, again? It's weird that it took you "several months" to balance your TB's....it took me several minutes. Also weird that you supposedly owned multiple CFI...yet you clearly don't know or understand how they actually work. Weird. Maybe you only owned them for a few minutes?

I'm not going to argue with you about vans or Datsuns....you should avoid arguing with CFI owners about CFI. It makes you look dumb, and your giving the OP what we call, "Bad advice". OP probably wants GOOD advice.

It's unfortunate that you had so much struggle with your CFI cars...they're really quite easy to own, work on, and they run great -when you understand how they work.

Actually balancing them did not take long, once I understood the throttle shafts were leaking, the IACs were shot and the injectors were in the wrong TBIs on one and the other had flat out wrong injectors. I absolutely understand how they worked. I kept the Vette for 2 years with it and the family C10 is still around and running with a well setup CFI system although I gave it to my sister.

O.K.

I apologize if im late to revive this thread. But I've had a similar issue on my 89. No service light at all. It would always idle too high and at some points it would surge at idle. More so if it was engaged in gear. Drive or reverse. It got soo bad that the car refused to start after it was warmed up. We assumed the started was getting cooked or the ignition module got too hot. Then the surge got soo bad that the car would want to lurch forward when I was at a stop light holding onto the brake. I eventually started to noticed that my voltmeter was displaying erratic behavior. As well as my gauges. Sourced the problem to a bad battery ground cable. According to rhe shop manual. A bad ground can cause the iac valve to behave erratically and cause some idle surges. Because it thinks it needs to compensate? Just a weird observation I made. Not saying it may be your solution but even I was surprised a simple electrical snafu could create a gremlin that big.